Same here. Upgraded my Ubuntu 16.04 LTS. After the upgrade only some of my QT apps work. Stipend wallet works but Apollon and Deviant do not open at all.

Since the update I'm also having high CPU usage in Openbox. Logs are filliing up with Print error while x2go is running. If I close x2go CPU usage is normal and error reporting stops.

Here is the .xsession-x2go-errors log of a failed QT app that doesn't open nestled in the gazillion Openbox messages that occur running x2go:

Openbox-Message: Requested key "Print" does not exist on the display
Openbox-Message: Requested key "Print" does not exist on the display
Openbox-Message: Requested key "Print" does not exist on the display
Openbox-Message: Requested key "Print" does not exist on the display
Openbox-Message: Requested key "Print" does not exist on the display
XIO: fatal IO error 0 (Success) on X server ":50"
after 280 requests (278 known processed) with 0 events remaining.
Openbox-Message: Requested key "Print" does not exist on the display
Openbox-Message: Requested key "Print" does not exist on the display
Openbox-Message: Requested key "Print" does not exist on the display
Openbox-Message: Requested key "Print" does not exist on the display