Main: Custom Parts can't be made visible

[zacjansheski]

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

1. Make a score with two instruments
2. Make a custom part
3. Try to make instruments visible

Supporting files, videos and screenshots

video1844280302.mp4

In which versions of MuseScore Studio is this issue present?

OS: macOS Tahoe (26.5.1), Arch.: arm64, MuseScore Studio version (64-bit): 5.0.0-260713041, revision: github-musescore-musescore-83bc55b

Regression

Yes, this works in the latest released version and is broken in the nightly builds

Operating system

MacOS Tahoe 26.2

Additional context

No response

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