The general syslog, after enabling server debug output, and client debug output (x2goclient --debug) is more important, but this issue looks a lot like https://github.com/ArcticaProject/nx-libs/issues/679
I've only fixed the screen positioning issue today - nightly builds should already have that fix.
A workaround is to start x2goclient on your first (normally also primary) display. Are you starting it on a secondary (non-first) display? If yes, then it's likely that this is causing the trouble.
After skimming your original post again, I also wonder if you have partly upgraded packages on that machine.
dpkg -l | grep -Ei '(x2go|nx)'
Mihai