Black and inaccessible floating windows

[moritzschaefer]

It happens to me once in a while that EXWM starts to fail to properly show floating windows (e.g. file save dialog). These then appear as black boxes (in the size of the dialog that's supposed to be there). There is no way to interact with these dialogs (so I can also not make them tiling again), but I can kill the buffer, which makes them disappear (and also unfreeze the associated X application).

Unfortunately, once this happens the first time, emacs is "locked" in a state, in which this always happens to floating windows, so I need to restart Emacs to fix it.

Can I provide any debug information to pinpoint the issue?