Start Center black and GUI partially broken (3.3 beta 2 Linux)

A few days before I mounted the Linux AppImage of MuseScore 3.3 beta 2 version, and I tried to launch it, but the GUI seems broken. The Start Center is black, and the palettes on the left are broken (see attatched screenshot). What's more, I was working on a dialog plugin which does not work now, because it started with a dialog window with some options that are now no longer visible (the window is just blank, but if I guess where the -invisible- buttons are and press them, they work). The only thing I can think of that might have caused this is some update (I was using this version of MuseScore from the AppImage provided for some time before). Any ideas?