dovecot - Jul 2019 - Warning: Failed to do incremental sync

Setup dovecot sync along the lines of (https://wiki2.dovecot.org/Replication). 
I am doing one way replication.

The initial full replication happened without issue, but now I'm seeing
these errors on the slave server:

doveadm: Warning: /data/mail/foo/bar/Maildir/dovecot-uidlist: Duplicate file
entry at line 26397: 1562173159.M215923P17350.mxp,S=2290,W=2339 (uid 143128
-> 143142)

Warning: Failed to do incremental sync for mailbox Sent Messages, retry with a
full sync (Modseq 1766 no longer in transaction log (highest=17617,
last_common_uid=17559, nextuid=17560))

Warning: Failed to do incremental sync for mailbox INBOX, retry with a full sync
(Modseq 2540 no longer in transaction log (highest=13870, last_common_uid=19912,
nextuid=19913))



I guess dovecot automatically tries a full replication because eventually the
messages get pushed and "sync failed" status changes from 'y'
to '-'

I am getting a lot of these messages (on the master side of replication)? :
dovecot: doveadm: Error: dsync-remote(userxyz): Warning: Failed to do 
incremental sync for mailbox INBOX, retry with a full sync (Modseq 81589 
no longer in transaction log)

Having "Error" and "Warning" on the same line is confusing,
to start with.
If I get it right. it means that very often (incremental) sync fails and 
replication starts again after 5 min? but this time by doing full sync, 
which, I guess, is not good (more resources used).
Since I am doing only one way replication what could be the reason for 
those errors/warnings? Nothing is changing files on the remote side 
besides dsync-server.
Is there anything I can do to "fix" this ?


# dovecot --version
2.2.33.2 (d6601f4ec)