I think this only showed up after updating to 2.17. Not sure what all causes it to happen at this point

Atleast have it happen most times I reopen Mixo

Are the keys in white? That means they are in an unknown format and failed to get converted.

Please can you send me a screenshot of the keys that are not converting, in the track list?

Screenshot right after opening Mixo showing keys in Open. Settings show Musical. And then after closing settings keys show as Musical. Didn't even touch the setting just opened up the settings screen and went back to the library.

Replicated, thanks.

Fixed, will be in the next release. Maybe a beta before! Thanks :)