This IS the issue. The Main Menu popout can cause issues for multi-monitors and VR users....but I should have it show by default, MY BAD, I'm sorry.....how to correct....
You can access the Settings/Pref GUI via X-Plane's own menu as shown below OR....by the new commands I provided HERE. (See ADDED section)
Plugins > Gizmo64 > Windows > IXEG 737 Classic.
From there, select the preference panel and UNCHECK the box that says "Disable Main menu Popout"....from there you should be good with the Main Menu Popout.
So sorry folks.
TK