SSH freezes when idle for a time
on the connecting client, in /etc/ssh/ssh_config, try:
ServerAliveInterval 60
not sure why the ClientAliveInterval is not working for you on the server.... maybe you need to restart sshd, if you did not do so after adding the ClientAliveInterval directive?
if you do not have root on the client, you can stick the ServerAliveInterval in
~/.ssh/config