Re: An I/O error occurred while sending to the backend (PG 13.4)

You originally mailed about an error on the client, and now you found
corresponding server logs, which suggests a veritable network issue.

Are the postgres clients and server on the same subnet ?  If not, what are the
intermediate routers ?  Is there any NAT happening ?  Do those devices have any
interesting logs that correspond with the server/client connection failures ?

Have you tried enabling TCP keepalives ?  This might help to convince a NAT
device not to forget about your connection.

https://www.postgresql.org/docs/current/runtime-config-connection.html
tcp_keepalives_idle=9
tcp_keepalives_interval=9
tcp_keepalives_count=0
tcp_user_timeout=0 -- You apparently have this set, but it cannot work on windows, so just generates noise.

On linux, you can check the keepalive counters in "netstat -not" to be sure
that it's enabled.  A similar switch hopefully exists for windows.

-- 
Justin