MediaMonkey not reliably writing Metadata into files

[BunnyGandhi]

It seems like MediaMonkey only sometimes actually writes the MetaData into the files.

I'm on Windows10, using MediaMonkey 5.1.0.2832
Handling exclusively .mp4 video files and curating the fields "Genre", "Title" and "Producers" for MetaData

Changing MetaData within MediaMonkey and then saving the changes (ctrl+s on selected file) will
1. Reliably (pretty sure, have not found an exception) apply the input of the "Producers" field to the .mp4 file
2. Most of the time (like 9/10) not apply the "Genre" and "Title" input to the .mp4 file. But it DOES work on some. (best type of bug, right?)

Same problem with old files as with entirely freshly created ones (so 0 chance of the freshly created file to be damaged, an .avi renamed to .mp4 or shenanigans like that)

So a few of my files actually get the updated MetaData while most of them only get one field updated. For the Star Rating I don't even need to do ctrl+S to update it in the file, that happens in real time. But for the Genre and Title field it seems to be a total coin toss. Tried if it's maybe field limitations (title too long) or if just changing anything sends the update and makes it work but to no avail.

Ideas?

More interestingly: If I manually type in e.g. the Genre field on one of those files and then rescan the library with MediaMonkey, MM will actually remove my entry from the field sO I'm really lost on what this problem could even be...

[Lowlander]

How are you verifying that the fields are not being updated? It may be a case of having multiple tags for the same field in the file and different softwares reading different tags.