Filebeat System module not sending process name when using Logstash as a output

I am using filebeat system module to send syslog data to Elasticsearch and it is working fine, even the default dashboard is also working fine. However, while I use Logstash as the output, it is not sending few fields such as process name and therefore it's not mapping with dashboard visualizations.

What versions of Filebeat, Logstash, and Elasticsearch are you running?

Also, would you mind re-running Filebeat with logging.level: debug? This will let us see JSON representations of events that Filebeat is sending to Logstash.

Thanks,

Shaunak

Filebeat: 6.8
Logstash: 7.9.2
Elasticsearch: 7.9.2

Here is my filebeat.yml

###################### Filebeat Configuration Example #########################

# This file is an example configuration file highlighting only the most common
# options. The filebeat.reference.yml file from the same directory contains all the
# supported options with more comments. You can use it as a reference.
#
# You can find the full configuration reference here:
# https://www.elastic.co/guide/en/beats/filebeat/index.html

# For more available modules and options, please see the filebeat.reference.yml sample
# configuration file.
#display_name
# ============================== Filebeat inputs ===============================

filebeat.inputs:

# Each - is an input. Most options can be set at the input level, so
# you can use different inputs for various configurations.
# Below are the input specific configurations.

- type: log

  # Change to true to enable this input configuration.
  enabled: true

  # Paths that should be crawled and fetched. Glob based paths.
  paths:
    - /var/log/syslog
    #- c:\programdata\elasticsearch\logs\*

  # Exclude lines. A list of regular expressions to match. It drops the lines that are
  # matching any regular expression from the list.
  #exclude_lines: ['^DBG']

  # Include lines. A list of regular expressions to match. It exports the lines that are
  # matching any regular expression from the list.
  #include_lines: ['^ERR', '^WARN']

  # Exclude files. A list of regular expressions to match. Filebeat drops the files that
  # are matching any regular expression from the list. By default, no files are dropped.
  #exclude_files: ['.gz$']

  # Optional additional fields. These fields can be freely picked
  # to add additional information to the crawled log files for filtering
  #fields:
  #  level: debug
  #  review: 1

  ### Multiline options

  # Multiline can be used for log messages spanning multiple lines. This is common
  # for Java Stack Traces or C-Line Continuation

  # The regexp Pattern that has to be matched. The example pattern matches all lines starting with [
  #multiline.pattern: ^\[

  # Defines if the pattern set under pattern should be negated or not. Default is false.
  #multiline.negate: false

  # Match can be set to "after" or "before". It is used to define if lines should be append to a pattern
  # that was (not) matched before or after or as long as a pattern is not matched based on negate.
  # Note: After is the equivalent to previous and before is the equivalent to to next in Logstash
  #multiline.match: after

# ============================== Filebeat modules ==============================

filebeat.config.modules:
  # Glob pattern for configuration loading
  path: ${path.config}/modules.d/*.yml

  # Set to true to enable config reloading
  reload.enabled: false

  # Period on which files under path should be checked for changes
  #reload.period: 10s

# ======================= Elasticsearch template setting =======================

setup.template.settings:
  index.number_of_shards: 1
  #index.codec: best_compression
  #_source.enabled: false


# ================================== General ===================================

# The name of the shipper that publishes the network data. It can be used to group
# all the transactions sent by a single shipper in the web interface.
#name:

# The tags of the shipper are included in their own field with each
# transaction published.
#tags: ["service-X", "web-tier"]

# Optional fields that you can specify to add additional information to the
# output.
#fields:
#  env: staging

# ================================= Dashboards =================================
# These settings control loading the sample dashboards to the Kibana index. Loading
# the dashboards is disabled by default and can be enabled either by setting the
# options here or by using the `setup` command.
#setup.dashboards.enabled: false

# The URL from where to download the dashboards archive. By default this URL
# has a value which is computed based on the Beat name and version. For released
# versions, this URL points to the dashboard archive on the artifacts.elastic.co
# website.
#setup.dashboards.url:

# =================================== Kibana ===================================

# Starting with Beats version 6.0.0, the dashboards are loaded via the Kibana API.
# This requires a Kibana endpoint configuration.
setup.kibana:

  # Kibana Host
  # Scheme and port can be left out and will be set to the default (http and 5601)
  # In case you specify and additional path, the scheme is required: http://localhost:5601/path
  # IPv6 addresses should always be defined as: https://[2001:db8::1]:5601
  host: "https://kibana.app:5601"
  username: "uname"
  password: "password"
  # Kibana Space ID
  # ID of the Kibana Space into which the dashboards should be loaded. By default,
  # the Default Space will be used.
  #space.id:

# =============================== Elastic Cloud ================================

# These settings simplify using Filebeat with the Elastic Cloud (https://cloud.elastic.co/).

# The cloud.id setting overwrites the `output.elasticsearch.hosts` and
# `setup.kibana.host` options.
# You can find the `cloud.id` in the Elastic Cloud web UI.
#cloud.id:

# The cloud.auth setting overwrites the `output.elasticsearch.username` and
# `output.elasticsearch.password` settings. The format is `<user>:<pass>`.
#cloud.auth:

# ================================== Outputs ===================================

# Configure what output to use when sending the data collected by the beat.

# ---------------------------- Elasticsearch Output ----------------------------
#output.elasticsearch:
  # Array of hosts to connect to.
  #hosts: ["localhost:9200"]

  # Protocol - either `http` (default) or `https`.
  #protocol: "https"

  # Authentication credentials - either API key or username/password.
  #api_key: "id:api_key"
  #username: "elastic"
  #password: "changeme"

output.elasticsearch:
  # Array of hosts to connect to.
   hosts: ["ip:9200"]

  # Protocol - either `http` (default) or `https`.
   protocol: "https"
   ssl.verification_mode: none
  # Authentication credentials - either API key or username/password.
  #api_key: "id:api_key"
   username: "uname"
   password: "password"

# ------------------------------ Logstash Output -------------------------------
#output.logstash:
  # The Logstash hosts
  #hosts: ["ip:5044"]

  # Optional SSL. By default is off.
  # List of root certificates for HTTPS server verifications
  #ssl.certificate_authorities: ["/etc/pki/root/ca.pem"]

  # Certificate for SSL client authentication
  #ssl.certificate: "/etc/pki/client/cert.pem"

  # Client Certificate Key
  #ssl.key: "/etc/pki/client/cert.key"

# ================================= Processors =================================

# Configure processors to enhance or manipulate events generated by the beat.

processors:
  - add_host_metadata: ~
  - add_cloud_metadata: ~
  - add_docker_metadata: ~
  - add_kubernetes_metadata: ~


# ================================== Logging ===================================

# Sets log level. The default log level is info.
# Available log levels are: error, warning, info, debug
logging.level: debug

# At debug level, you can selectively enable logging only for some components.
# To enable all selectors use ["*"]. Examples of other selectors are "beat",
# "publish", "service".
#logging.selectors: ["*"]

# ============================= X-Pack Monitoring ==============================
# Filebeat can export internal metrics to a central Elasticsearch monitoring
# cluster.  This requires xpack monitoring to be enabled in Elasticsearch.  The
# reporting is disabled by default.

# Set to true to enable the monitoring reporter.
#monitoring.enabled: false

# Sets the UUID of the Elasticsearch cluster under which monitoring data for this
# Filebeat instance will appear in the Stack Monitoring UI. If output.elasticsearch
# is enabled, the UUID is derived from the Elasticsearch cluster referenced by output.elasticsearch.
#monitoring.cluster_uuid:

# Uncomment to send the metrics to Elasticsearch. Most settings from the
# Elasticsearch output are accepted here as well.
# Note that the settings should point to your Elasticsearch *monitoring* cluster.
# Any setting that is not set is automatically inherited from the Elasticsearch
# output configuration, so if you have the Elasticsearch output configured such
# that it is pointing to your Elasticsearch monitoring cluster, you can simply
# uncomment the following line.
#monitoring.elasticsearch:

# ================================= Migration ==================================

# This allows to enable 6.7 migration aliases
#migration.6_to_7.enabled: true

here is my system.yml

  # Module: system
            # Docs: https://www.elastic.co/guide/en/beats/filebeat/7.8/filebeat-module-system.html

            #- module: system
              # Syslog
             # syslog:
               # enabled: true

                # Set custom paths for the log files. If left empty,
                # Filebeat will choose the paths depending on your OS.
               # var.paths: ["/var/log/syslog"]
               # var.convert_timezone: true
              # Authorization logs
              #auth:
                #enabled: true

                # Set custom paths for the log files. If left empty,
                # Filebeat will choose the paths depending on your OS.
                #var.paths: ["/var/log/auth"]
                #var.convert_timezone: true

here is my filebeat logfile

2021-02-01T12:47:54.003Z        INFO    instance/beat.go:647    Home path: [/usr/share/filebeat] Config path: [/etc/filebeat] Data path: [/var/lib/filebeat] Logs path: [/var/log/filebeat]
2021-02-01T12:47:54.003Z        INFO    instance/beat.go:655    Beat ID: accaa3df-79c3-48b4-9660-58e14cbe29e1
2021-02-01T12:47:54.005Z        INFO    [beat]  instance/beat.go:983    Beat info       {"system_info": {"beat": {"path": {"config": "/etc/filebeat", "data": "/var/lib/filebeat", "home": "/usr/share/filebeat", $
2021-02-01T12:47:54.005Z        INFO    [beat]  instance/beat.go:992    Build info      {"system_info": {"build": {"commit": "f79387d32717d79f689d94fda1ec80b2cf285d30", "libbeat": "7.8.0", "time": "2020-06-14T1$
2021-02-01T12:47:54.005Z        INFO    [beat]  instance/beat.go:995    Go runtime info {"system_info": {"go": {"os":"linux","arch":"amd64","max_procs":2,"version":"go1.13.10"}}}
2021-02-01T12:47:54.005Z        INFO    [beat]  instance/beat.go:999    Host info       {"system_info": {"host": {"architecture":"x86_64","boot_time":"2021-02-01T12:03:19Z","containerized":false,"name":"ip-172-$
2021-02-01T12:47:54.005Z        INFO    [beat]  instance/beat.go:1028   Process info    {"system_info": {"process": {"capabilities": {"inheritable":null,"permitted":["chown","dac_override","dac_read_search","fo$
2021-02-01T12:47:54.005Z        INFO    instance/beat.go:310    Setup Beat: filebeat; Version: 7.8.0
2021-02-01T12:47:54.006Z        INFO    [index-management]      idxmgmt/std.go:183      Set output.elasticsearch.index to 'filebeat-7.8.0' as ILM is enabled.
2021-02-01T12:47:54.006Z        INFO    eslegclient/connection.go:97    elasticsearch url: https://localhost:9200
2021-02-01T12:47:54.006Z        WARN    [tls]   tlscommon/tls_config.go:83      SSL/TLS verifications disabled.
2021-02-01T12:47:54.006Z        INFO    [publisher]     pipeline/module.go:113  Beat name: ip-172-21-6-100
2021-02-01T12:47:54.007Z        INFO    eslegclient/connection.go:97    elasticsearch url: https://localhost:9200
2021-02-01T12:47:54.007Z        WARN    [tls]   tlscommon/tls_config.go:83      SSL/TLS verifications disabled.
2021-02-01T12:47:54.007Z        WARN    [tls]   tlscommon/tls_config.go:83      SSL/TLS verifications disabled.
2021-02-01T12:47:54.012Z        INFO    [add_cloud_metadata]    add_cloud_metadata/add_cloud_metadata.go:93     add_cloud_metadata: hosting provider type detected as aws, metadata={"account":{"id":"6551364$
2021-02-01T12:47:54.113Z        INFO    [esclientleg]   eslegclient/connection.go:306   Attempting to connect to Elasticsearch version 7.9.1
2021-02-01T12:47:54.132Z        INFO    [index-management]      idxmgmt/std.go:259      Auto ILM enable success.
2021-02-01T12:47:54.133Z        INFO    [index-management.ilm]  ilm/std.go:139  do not generate ilm policy: exists=true, overwrite=false
2021-02-01T12:47:54.133Z        INFO    [index-management]      idxmgmt/std.go:272      ILM policy successfully loaded.
2021-02-01T12:47:54.133Z        INFO    [index-management]      idxmgmt/std.go:405      Set setup.template.name to '{filebeat-7.8.0 {now/d}-000001}' as ILM is enabled.
2021-02-01T12:47:54.133Z        INFO    [index-management]      idxmgmt/std.go:410      Set setup.template.pattern to 'filebeat-7.8.0-*' as ILM is enabled.
2021-02-01T12:47:54.133Z        INFO    [index-management]      idxmgmt/std.go:444      Set settings.index.lifecycle.rollover_alias in template to {filebeat-7.8.0 {now/d}-000001} as ILM is enabled.
2021-02-01T12:47:54.133Z        INFO    [index-management]      idxmgmt/std.go:448      Set settings.index.lifecycle.name in template to {filebeat {"policy":{"phases":{"hot":{"actions":{"rollover":{"max_age":"3$
2021-02-01T12:47:54.143Z        INFO    template/load.go:169    Existing template will be overwritten, as overwrite is enabled.
2021-02-01T12:47:54.411Z        INFO    template/load.go:109    Try loading template filebeat-7.8.0 to Elasticsearch
2021-02-01T12:47:54.565Z        INFO    template/load.go:101    template with name 'filebeat-7.8.0' loaded.
2021-02-01T12:47:54.565Z        INFO    [index-management]      idxmgmt/std.go:296      Loaded index template.
2021-02-01T12:47:54.786Z        INFO    [index-management]      idxmgmt/std.go:307      Write alias successfully generated.
2021-02-01T12:47:54.786Z        INFO    kibana/client.go:118    Kibana url: https://localhost:5061
2021-02-01T12:49:24.786Z        ERROR   instance/beat.go:958    Exiting: error connecting to Kibana: fail to get the Kibana version: HTTP GET request to https://localhost:5061/api/status fails: fail to exe$

While syslog is being sent directly to Elasticsearch it sends process.name field, but when I switch filebeat output to Logstash, it stops sending process.name. I identify this one field but there may be many fields like such which are not coming when logs are coming via Logstash.