Disappearing menubar

When I launched Cubase Pro a couple of days ago, the splash screen was replaced with this;
Instead of Splashscreen.png
When Cubase Pro was finished launching, the main menubar was missing:

Reinstalling Cubase got the splashscreen back, but not the menus. I’ve even tried rebuilding the entire preferences folder, to no avail. This only affects Cubase Pro. No other software is affected, including my other Steinberg software (Wavelab Elements, Halion 6, etc.) Note that context (right clicking) menus are still there, Only the main menubar is absent.

This is, of cause, a very serious problem. Without access to the menus, Cubase is unusable. And because my entire studio is revolving around Cubase Pro, the whole studio is unusable.

Any assistance with what might be causing this, and how to fix it, would be greatly appreciated.