Why can some clients connect to the host via ssh, while others have a problem - ssh freezes?

Question

SSH

I can’t unearth the reason for this behavior: some clients can connect to the host via ssh, while others have a problem - ssh hangs at the debug1 connecting to host stage, can you tell me which way to dig?
I thought that the problem was in the version of ssh clients: but out of two clients with the same version of ssh, OS and the same external ip, one can connect, and the second hangs.
I also tried to play with the parameters:

TCPKeepAlive yes
ClientAliveInterval 120

Host *
TCPKeepAlive yes
ServerAliveInterval 30

Did not help.
On an Ubuntu 16.04 host, on clients, different OSes (from desktop Ubuntu 16.04 to Centos 7), some connect, others freeze. I can not understand the reason for this behavior, maybe you can tell me from personal experience how to solve such a trouble?

Answer 1

Enable the -vvv option and watch the logs. Most likely the list of available encryption methods is different.

Answer 2

MTU on client interfaces what?