On MacOS, shortcuts will be disabled if pressed when using non-roman-alphabet-based IME (input method editor).
Steps to reproduce:
1. On Mac, set up any input method using a non-roman-alphabet-based IME, for example, Zhuyin, Japanese(Hiragana), Hangul, etc. Using roman-alphabet-based ones (e.g., Pinyin, Japanese(Roman), ...) won't reproduce this issue.
2. Open Musescore, in one of those IMEs, try to use shortcuts. Shortcuts without using the control, option, or the command keys should be disabled once pressed. The only way to re-enable them is restarting Musescore.
3. As a sidenote, changing to English keyboard after the bug has happened does not solve the bug.
The bug almost always happens, but it does occasionally not happen.
Also, the Windows version of Musescore doesn't have this bug.