same problem here. Afters hours (3-4H, random) , session becomes slow, clic very long to respond. No network problem, no load or CPU high on server, everything is normal on server.

I was unable to reproduce at any time. and i wad unable to guess what KDE4 app is problem. Application that are used :  Dolphin, Open Office Calc, sometimes Firefox

Closing session et restart it is OK.

I can make some tests or look for logs if you want..

Package: x2goserver

The client machine's OS: Window 7 or Linux Debian Jessie
The client machine's version of X2GoClient:
Any relevant session settings in X2GoClient: KDE 4.13 session
The server's OS: Ubuntu 14.04 64-bit
The server's version of the x2goserver package:
The server's version of the x2goserver-xsession package (included in
server package) :
The server's version of the nx-libs package: