I am only able to keep one session of x2go open at a time. When I start a new client, the first session terminates by itself. I restart it, and the other session terminates. These are to two separate hosts. On both ends is Debian Testing, kept current.
Could be a TCP port conflict. Try changing the value for SSH_PORT to 30200 in /usr/bin/x2gostartagent on one of the target machines so they are using different port ranges. End all X2Go sessions (not just disconnect, log out) before you try again.
Cheers, Daniel