Dsync issues since 2.3.11.3.

[Reio Remma]

Hello!

I've started seeing intermittent dsync failures since upgrading Dovecot 
to 2.3.11.3-3 (CentOS 8 using the official Dovecot repo).

Sep 27 17:49:04 host dovecot[130]: 
dsync-local(user at host)<5GWFD2CmcF+TJwAAsNnMGQ>: Warning: Failed to do 
incremental sync for mailbox INBOX, retry with a full sync (Modseq 66543 
no longer in transaction log (highest=66547, last_common_uid=46346, 
nextuid=46347))
Sep 27 17:49:04 host dovecot[130]: 
dsync-local(user at host)<5GWFD2CmcF+TJwAAsNnMGQ>: Error: Remote command 
returned error 75: ssh <options> doveadm dsync-server -u user at host

It seems to happen at random times to random users.

My setup has 2 servers - users are connecting to the main server and the 
secondary server is just for backup - noone is actually connecting to it.

Any suggestions?

Thanks!
Reio