With Finale closed, try clearing out (deleting) the files in Finale's Temp folder. The location of that folder should be listed in Edit > Preferences > Folders.

Many experienced users reset the location of that file to a more accessible location (I have mine in Documents/FinaleTempFiles) for easy access so one can clean it out on a regular basis.

On a Mac, it's not necessary to delete temp files. What often helps on a Mac is to delete your Finale preferences and restart Finale. If that doesn't help, I'd suggest opening up a support ticket with MM.

Did it just happen once?

Forget about it, and move on. It happens to me on occasion, with no ill effects.

If it happens on every score, then it's an issue that you should take up with MM.