ssh: broken pipe immediately after successful login

I have two servers that (at least at one point) were identical and working fine. Ubuntu 18.04Server pl2poland is a backup server for pl3poland and hosts a replication PostgreSQL database.We use the Admin user "invadm" to log on to both servers using SSH.

For some reason, the pl2poland server suddenly has started giving us broken pipe messages when you try to log on as the invadm user.

This message shows up when I try to SSH to pl2poland from other servers:

$ ssh invadm@pl2polandinvadm@pl2poland's password:Write failed: Broken pipe

I do have other logins that work on pl2poland, but if I try to ssh from any user (even root) on pl2poland to the invadm user, I get this slightly different error:

root@pl2poland: ssh invadm@pl2polandinvadm@pl2poland's password:packet_write_wait: Connection to 192.168.23.5 port 22: Broken pipe

I believe that there must be an issue with that specific user, but I've tried various things and cannot track down a fix for it. The other questions I've seen here all suggest a timeout may be happening and to adjust settings in /etc/ssh/ssh_config. But this is happening immediately, not after a few minutes of idle time.

Here is a what happens within ssh -vv messages at the point where I enter the password. It is a valid password (confirmed) and the ssh even says "Authentication Succeeded", but then kicks us out.

debug1: Authentications that can continue: publickey,passworddebug1: Trying private key: /.ssh/id_dsadebug1: Trying private key: /.ssh/id_ecdsadebug2: we did not send a packet, disable methoddebug1: Next authentication method: passwordinvadm@pl2poland's password:debug2: we sent a password packet, wait for replydebug1: Authentication succeeded (password).Authenticated to pl2poland ([192.168.23.5]:22).debug1: channel 0: new [client-session]debug2: channel 0: send opendebug1: Requesting no-more-sessions@openssh.comdebug1: Entering interactive session.Write failed: Broken pipe

I tried changing the password, checking permissions on /home/invadm and /home/invadm/.ssh, tried a suggestion to use "ssh -o IPQoS=throughput". Nothing seems to make a difference.

Can someone point me to a file to check or an article to read that maybe I did not spot yet?

Thanks,

Steve N.