ssh connections break with "Fssh_packet_write_wait" on 13

Hi,

Since upgrading servers from 12.2 to 13.0, I get

  Fssh_packet_write_wait: Connection to 1.2.3.4 port 22: Broken pipe

consistently, usually after about 11 idle minutes, that's with and
without pf enabled. Client (11.4 in a VM) wasn't altered.

Verbose logging (client and server side) doesn't show anything special
when the connection breaks. In the past, QoS problems caused these
disconnects, but I didn't see anything apparent changing between 12.2
and 13 in this respect.

I did a test on a newly commissioned server to rule out other factors
(so, same client connections, some routes, same everything). On 12.2
before the update: Connection stays open for hours. After the update
(same server): connections breaks consistently after < 15 minutes (this
is with unaltered configurations, no *AliveInterval configured on
either side of the connection).

Thanks
Michael

-- 
Michael Gmelin