2.3.1 Replication is throwing scary errors

Hi

[This is Dovecot 2.3.1 at FreeBSD STABLE-11.1 running in two jails at distinct servers.]

I did upgrade from 2.2.35 to 2.3.1 today, and I do become pounded by error messages at server1 (and vice versa at server2) as follows:

| Apr  2 17:12:18 <mail.err> server1.lan dovecot: doveadm: Error: dsync(server2.lan): I/O has stalled, \
	no activity for 600 seconds (last sent=mail_change, last recv=mail_change (EOL))
| Apr  2 17:12:18 <mail.err> server1.lan dovecot: doveadm: Error: Timeout during state=sync_mails \
	(send=changes recv=mail_requests)
[…]
| Apr  2 18:59:03 <mail.err> server1.lan dovecot: doveadm: Error: dsync(server2.lan): I/O has stalled, \
	no activity for 600 seconds (last sent=mail, last recv=mail (EOL))
| Apr  2 18:59:03 <mail.err> server1.lan dovecot: doveadm: Error: Timeout during state=sync_mails \
	(send=mails recv=recv_last_common)

I cannot see in my personal account any missing replications, *but* I haven't tested this thoroughly enough. I do have customers being serviced at these productive servers, *thus* I'm back to 2.2.35 until I do understand or have learned what is going on.

Any ideas/feedback?

FYI: I haven't seen such errors before. Replication has been working for years now, without any glitches at all.

Regards, Michael