How to investigate massive dropping of subscriptions?

I have docker EMQX 5.3.0 mqtt broker and several python (paho.mqtt) publishers and subscribers.
Several times of day i have massive drop of subscriptions and disconnection of python mqtt clients with error MQTT_ERR_KEEPALIVE.
You can see it in EMQX Cluster overview screenshot:

How can i investigate this problem by EMQX?
I tried to set up rule on event “client_disconnected” and “session_unsubscribed” with console output, but there are now logs for such events near problem timestamps.


This command can show more detailed info about disconnect statistics: EMQX FAQ | EMQX Documentation

If I had to guess, this problem is likely due to idle connections. If the clients are not sending or receiving any data for a very long time, either EMQX will drop connections as idle, or the underlying operating system will close TCP connections. The solution to both problem is to decrease the keep alive interval on the client to some reasonable value.