Lagging in ELK stack

Hi Experts,

I'm using ELK stack in docker environment:
logstash_syslog:7.4.0
Elasticsearch:7.1
kibana:7.1

Sometimes observe lagging of logs in kibana dashboard.

After 2/3 hours, it becomes adjusted. Lagging usually appears in busy hours.

Use filebeat(7.1.1) in different nodes which usually ship nginx log, container logs, application logs etc to logstash.

How can I troubleshoot this issue? What are the things that I should look for?
Please help me.

Regards.

Any reason why you are running outdated versions ?

A lot of performance gain can be attributed to just an upgrade!

No reason....update soon.
Any kind of troubleshooting and optimization do you suggest on this version?