Scenario is forwarding authentication by using the SSH Pageant agent to a NoMachine Linux session in order to use the authentication in a script.

To reproduce the problem:

1. Connect by NoMachine using SSH protocol + "Use key-based authetication with a SSH agent" + Forward authetication

2. Create a custom session in floating window mode with xterm or another terminal

3. inside terminal execute this loop:
for i in {1..100}; do ssh localhost 'uptime'; done

About 20-50 interaction work properly. After that, the session is disconnected and then automatically reconnected but it asks for pasword to authenticate.

A possible workaround could be to add a sleep of 1-2 seconds between one interaction and the others.