To Reproduce
Steps to reproduce the behavior:
Case 1:
- Open Big_Score.zip
- Open Mixer
- Start Playback
- Close-Open Mixer multiple times (see video below)
UPDATE (23 Mar 2022): Now it is harder to reproduce the crash: you need to close-open Mixer ~20 times instead of ~5.
Reducing priority.
Case 2 (fixed in #14790, can be tested on Mac for now):
- Open Big_Score.zip
- Open Mixer
- Start Playback
- Close-Open Mixer multiple times
- Stop Playback
- Close score (not MS app)

Desktop:
- OS: Win10/Mac11
 (didn't try on Linux)
Additional context
Sometimes can happen after first closing of Mixer (on big scores)