Imported BWW files don't play

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

1. Load a .bww file (like the attached)
2. Play

=> It doesn't sound at all, playback cursor moves though

3. Check the Mixer

=> It shows the Metronome only

4. Save (as .mscz)
5. Close
6. Reopen
7. Play

=> it Plays

8. Check the Mixer

=> It shows there now

Supporting files, videos and screenshots

Cabar Feidh.zip

In which versions of MuseScore Studio is this issue present?

Since at least 4.0.1, I don't have earlier 4.x version to test with

Regression

Yes, this used to work in MuseScore 3.x and now is broken

Operating system

Windows 11, but I don't think that matters?

Additional context

Stems from https://musescore.org/en/node/395339

Checklist

• This report follows the guidelines for reporting bugs and issues
• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
• I have attached all requested files and information to this report
• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible

Use the attached Cabar Feidh.zip and reproduce the .bww import, playback, mixer, save, close, and reopen sequence. Compare the initial imported state with the reopened .mscz state; done means imported BWW playback produces sound and its instruments appear in the Mixer before saving.