Mobaxterm connects to Ubuntu server through SSH network error: software caused connection abort

MobaXterm v21.1 connects to Ubuntu 20.04.3 LTS server through SSHdisconnects all the time after short idle time, with this error:network error: software caused connection abort.I tried everything written here: https://programmerah.com/mobaxterm-connects-to-ubuntu-server-through-ssh-network-error-software-caused-connection-abort-43897/

• changed setting of Mobaextrem to keep alive
• edited /etc/ssh/sshd_config
  • TCPKeepAlive yes
  • ClientAliveInterval 60

I even left a top command running in the terminal, didn't help.

Is there an option that the disconnect is coming from the Ubuntu side ?Any idea how to solve it will be much appreciated.

** edit **

checking /var/log/auth.log

I see:

Mar  3 01:12:09 COSDEVVIS12 sshd[1529012]: Timeout, client not responding from user naomi <myip> port 59737

Beginning of /etc/ssh/sshd_config is:

#       $OpenBSD: sshd_config,v 1.103 2018/04/09 20:41:22 tj Exp $# This is the sshd server system-wide configuration file.  See# sshd_config(5) for more information./etc/ssh/sshd_config.d/*.conf

I run

/usr/sbin/sshd -ddd -p 10022

I get:

/etc/ssh/sshd_config: line 5: Bad configuration option: /etc/ssh/sshd_config.d/*.conf

...

/etc/ssh/sshd_config: terminating, 1 bad configuration options