Oh, I have the very similar problem now: when i choose in settings to show lxpanel at the bottom, i don't see it (it seems to me that it's drawn beyond the visible screen area), although the process is alive and working (Alt+F2 works, for example). If i choose to show it at the top of the desktop, it draws ok. It seems that x2goclient works incorrectly when you choose fixed resolution instead of fullscreen: x2goclient session window is declared as resizeable and when you resize it, lxpanel resizes, headers of maximized apps are resized too but the contents of their windows are not drawn beyond the initial area.
I don't remember but it seems that everything is OK when you choose fullscreen mode. Also, i remember that original NXClient session window is NOT resizeable when you select fixed resolution for session.