I am using version 7.8.1. I remember it being this way with a few previous versions as well. Here is what journalctl says. I run journalctl -f first, then edit a monitor from enabled: False to disabled: True, wait for half a minute and then restart the service manually to have it loaded. I remove many lines that simply count the events reported.
Sep 15 11:53:30 earth-kibana heartbeat[2998]: 2020-09-15T11:53:30.111Z        INFO        cfgfile/reload.go:224        Loading of config files completed.
Sep 15 11:53:30 earth-kibana heartbeat[2998]: 2020-09-15T11:53:30.241Z        DEBUG        [elasticsearch]        elasticsearch/client.go:229        PublishEvents: 50 events have been published to elasticsearch in 108.02437ms.
Sep 15 11:53:33 earth-kibana heartbeat[2998]: 2020-09-15T11:53:33.945Z        WARN        [tls]        tlscommon/tls_config.go:83        SSL/TLS verifications disabled.
Sep 15 11:53:33 earth-kibana heartbeat[2998]: 2020-09-15T11:53:33.985Z        DEBUG        [elasticsearch]        elasticsearch/client.go:229        PublishEvents: 50 events have been published to elasticsearch in 551.713238ms.
Sep 15 11:53:38 earth-kibana heartbeat[2998]: 2020-09-15T11:53:38.930Z        WARN        [tls]        tlscommon/tls_config.go:83        SSL/TLS verifications disabled.
Sep 15 11:53:38 earth-kibana heartbeat[2998]: 2020-09-15T11:53:38.994Z        DEBUG        [elasticsearch]        elasticsearch/client.go:229        PublishEvents: 50 events have been published to elasticsearch in 132.151003ms.
Sep 15 11:53:57 earth-kibana heartbeat[2998]: 2020-09-15T11:53:57.014Z        WARN        scheduler/scheduler.go:152        15 tasks have missed their schedule deadlines in the last 15s.
Sep 15 11:53:57 earth-kibana systemd[1]: Stopping Ping remote services for availability and log results to Elasticsearch or send to Logstash....
Sep 15 11:53:57 earth-kibana heartbeat[2998]: 2020-09-15T11:53:57.764Z        INFO        beater/heartbeat.go:120        Shutting down.
Sep 15 11:53:57 earth-kibana heartbeat[2998]: 2020-09-15T11:53:57.808Z        INFO        cfgfile/reload.go:227        Dynamic config reloader stopped
Sep 15 11:53:57 earth-kibana heartbeat[2998]: 2020-09-15T11:53:57.808Z        INFO        [reload]        cfgfile/list.go:118        Stopping 963 runners ...
Sep 15 11:53:57 earth-kibana heartbeat[2998]: 2020-09-15T11:53:57.863Z        INFO        [api]        api/server.go:66        Stats endpoint (192.168.1.5:5070) finished: accept tcp 192.168.1.5:5070: use of closed network connection
Sep 15 11:53:57 earth-kibana heartbeat[2998]: 2020-09-15T11:53:57.864Z        INFO        instance/beat.go:469        heartbeat stopped.
Sep 15 11:53:57 earth-kibana systemd[1]: Stopped Ping remote services for availability and log results to Elasticsearch or send to Logstash..
Sep 15 11:53:57 earth-kibana systemd[1]: Started Ping remote services for availability and log results to Elasticsearch or send to Logstash..
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.298Z        INFO        instance/beat.go:647        Home path: [/usr/share/heartbeat] Config path: [/etc/heartbeat] Data path: [/var/lib/heartbeat] Logs path: [/var/log/heartbeat]
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.308Z        INFO        instance/beat.go:655        Beat ID: 9805c7c4-6ede-5d01-92a3-2abe0d3960db
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.311Z        INFO        [api]        api/server.go:62        Starting stats endpoint
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.311Z        INFO        [seccomp]        seccomp/seccomp.go:124        Syscall filter successfully installed
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.313Z        INFO        [beat]        instance/beat.go:983        Beat info        {"system_info": {"beat": {"path": {"config": "/etc/heartbeat", "data": "/var/lib/heartbeat", "home": "/usr/share/heartbeat", "logs": "/var/log/heartbeat"}, "type": "heartbeat", "uuid": "9805c7c4-6ede-5d01-92a3-2abe0d3960db"}}}
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.314Z        INFO        [beat]        instance/beat.go:992        Build info        {"system_info": {"build": {"commit": "94f7632be5d56a7928595da79f4b829ffe123744", "libbeat": "7.8.1", "time": "2020-07-21T14:22:56.000Z", "version": "7.8.1"}}}
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.314Z        INFO        [api]        api/server.go:64        Metrics endpoint listening on: 192.168.1.5:5070 (configured: 192.168.1.5)
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.314Z        INFO        [beat]        instance/beat.go:995        Go runtime info        {"system_info": {"go": {"os":"linux","arch":"amd64","max_procs":2,"version":"go1.13.10"}}}
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.319Z        INFO        [beat]        instance/beat.go:999        Host info        {"system_info": {"host": {"architecture":"x86_64","boot_time":"2020-09-11T20:45:22Z","containerized":false,"name":"earth-kibana","ip":["127.0.0.1/8","::1/128","192.168.1.5/32","fe80::4001:c0ff:fea8:105/64"],"kernel_version":"5.0.0-1028-gcp","mac":["42:01:c0:a8:01:05"],"os":{"family":"debian","platform":"ubuntu","name":"Ubuntu","version":"18.04.3 LTS (Bionic Beaver)","major":18,"minor":4,"patch":3,"codename":"bionic"},"timezone":"UTC","timezone_offset_sec":0,"id":"e309c5fbad3714e4eb72cfbf36c8adaa"}}}
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.320Z        INFO        [beat]        instance/beat.go:1028        Process info        {"system_info": {"process": {"capabilities": {"inheritable":null,"permitted":["chown","dac_override","dac_read_search","fowner","fsetid","kill","setgid","setuid","setpcap","linux_immutable","net_bind_service","net_broadcast","net_admin","net_raw","ipc_lock","ipc_owner","sys_module","sys_rawio","sys_chroot","sys_ptrace","sys_pacct","sys_admin","sys_boot","sys_nice","sys_resource","sys_time","sys_tty_config","mknod","lease","audit_write","audit_control","setfcap","mac_override","mac_admin","syslog","wake_alarm","block_suspend","audit_read"],"effective":["chown","dac_override","dac_read_search","fowner","fsetid","kill","setgid","setuid","setpcap","linux_immutable","net_bind_service","net_broadcast","net_admin","net_raw","ipc_lock","ipc_owner","sys_module","sys_rawio","sys_chroot","sys_ptrace","sys_pacct","sys_admin","sys_boot","sys_nice","sys_resource","sys_time","sys_tty_config","mknod","lease","audit_write","audit_control","setfcap","mac_override","mac_admin","syslog","wake_alarm","block_suspend","audit_read"],"bounding":["chown","dac_override","dac_read_search","fowner","fsetid","kill","setgid","setuid","setpcap","linux_immutable","net_bind_service","net_broadcast","net_admin","net_raw","ipc_lock","ipc_owner","sys_module","sys_rawio","sys_chroot","sys_ptrace","sys_pacct","sys_admin","sys_boot","sys_nice","sys_resource","sys_time","sys_tty_config","mknod","lease","audit_write","audit_control","setfcap","mac_override","mac_admin","syslog","wake_alarm","block_suspend","audit_read"],"ambient":null}, "cwd": "/", "exe": "/usr/share/heartbeat/bin/heartbeat", "name": "heartbeat", "pid": 3068, "ppid": 1, "seccomp": {"mode":"filter","no_new_privs":true}, "start_time": "2020-09-15T11:53:57.570Z"}}}
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.320Z        INFO        instance/beat.go:310        Setup Beat: heartbeat; Version: 7.8.1
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.320Z        INFO        [index-management]        idxmgmt/std.go:184        Set output.elasticsearch.index to 'heartbeat-7.8.1' as ILM is enabled.
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.355Z        INFO        eslegclient/connection.go:99        elasticsearch url: https://35.206.159.154:9200
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.355Z        WARN        [tls]        tlscommon/tls_config.go:83        SSL/TLS verifications disabled.
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.355Z        INFO        eslegclient/connection.go:99        elasticsearch url: https://35.210.163.90:9200
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.355Z        WARN        [tls]        tlscommon/tls_config.go:83        SSL/TLS verifications disabled.
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.355Z        INFO        eslegclient/connection.go:99        elasticsearch url: https://35.210.170.219:9200
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.355Z        WARN        [tls]        tlscommon/tls_config.go:83        SSL/TLS verifications disabled.
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.356Z        INFO        [publisher]        pipeline/module.go:113        Beat name: earth-kibana-heartbeat
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.356Z        INFO        instance/beat.go:463        heartbeat start running.
Sep 15 11:53:58 earth-kibana heartbeat[3068]: 2020-09-15T11:53:58.356Z        INFO        beater/heartbeat.go:82        heartbeat is running! Hit CTRL-C to stop it.
Sep 15 11:54:00 earth-kibana heartbeat[3068]: 2020-09-15T11:54:00.236Z        INFO        cfgfile/reload.go:164        Config reloader started
Sep 15 11:54:00 earth-kibana heartbeat[3068]: 2020-09-15T11:54:00.466Z        ERROR        [reload]        cfgfile/list.go:96        Error creating runner from config: Monitor not loaded, plugin is disabled
Sep 15 11:54:00 earth-kibana heartbeat[3068]: 2020-09-15T11:54:00.468Z        ERROR        [reload]        cfgfile/list.go:96        Error creating runner from config: Monitor not loaded, plugin is disabled
Sep 15 11:54:00 earth-kibana heartbeat[3068]: 2020-09-15T11:54:00.469Z        ERROR        [reload]        cfgfile/list.go:96        Error creating runner from config: Monitor not loaded, plugin is disabled
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