Second Monitor = Lost Windows
The problem occurs when I've been working on two different monitors and then unplug my second monitor from my laptop. The mixer window that I've draged on my other monitor seems to stay jammed into the phantom screen. Restarting the program does not seem to fix the issue.
I haven't been testing this issue with all floating window, but it does that at least for the mixer one.
I work on Windows 10, but the problem also occured multiple times when I used to work on Windows 8.
Comments
The issue is known and will be fixed in the next major release by #120096: Some window size follow-ups.
In the meantime you could try if this plugin works for you: https://musescore.org/en/project/resetdialogpositions