Taking a guess, I would say your root partition is on some kind of flash memory, which doesn't like the constant writes, and eventually bugs out. Console messages should have something, or you could use remote syslog if console is not accessible for some reason.
It is on an ssd. So, I guess that might be a problem.
To mitigate the issue, I would suggest using tmpfs for /tmp - RAM does not wear out.
Could one specify where x2go keeps its tmp files? In that case, a separate tmpfs mount for it would solve the problem. Unless keeping all of /tmp on a tmpfs is recommended.
But your root media seems to already have issues, which will cause problems sooner or later in a different context.
Yes, I realise that. I hope running fsck on the root partition will fix that. I will look into it when I am on that system next.
Thanks a lot for all your advice.
V.