SSH link terminates every 20 seconds

I am using a 3rd party software to get an SSH link into my device ( I use Putty to SSH. All my other devices work but one device frequently loses SSH connection within 20 seconds but always remains online (I just can’t successfully stay logged in). Each device is on a separate network so I am assuming the router/firewall configuration is causing this. I would appreciate an explanation of what could possibly cause this. Thanks in advance!