X2GO client not forwarding keys like Ctrl and Alt
Solution 1:
I know this is old, but there was no answer... I found this, which worked for me (and others)
@glyndonwrote: For me (Ubuntu 17.10), the fix was to turn off the "show mouse pointer location when Ctrl key pressed."
I had to use dconf-editor to locate that setting, as Ubuntu no longer includes it on the regular settings dialog panel.
(in dconf-editor: org/gnome/settings-daemon/peripherals/mouse)