Hi,

What I would do… Turn on logging connections and disconnections in postgresql.conf file. There are two parameters for that which are set off by default.

log_connections = on
log_disconnections = on

Here is an official doc on it:
https://www.postgresql.org/docs/13/runtime-config-logging.html

Then, check logs and try to find any pattern which could lead you to the root cause.

If you connect your database through secure links (VPN, VPC etc.) you could turn off SSL to check if the error is related to this layer.