How can I analyze/replace MP4 tags which are not recognized?

I have loaded about 3000 music titles - most in AAC, some MP3 onto an SD-card for my car entertainment system (Mitsubishi ASX). All of them have tags - artist, album, title, genre, ... some of them also have embedded cover art. All of those tags can be nicely viewed and edited with Mp3tag.
BUT: only few of them are recognized by the entertainment system! There are some CDs on which everything is perfect and displayed in the car. For most, however, all I can see is the title (probably derived from the filename which usually is the title). No artist, no album, no genre, no album cover.

The MP3 files are easiest - it seems all MP3-files with their ID3 tags work well in the car. But most of my collection is AAC. And most of the MP4 tags do not work... However - I cannot find the difference (so those which are recognized in the car and those which are not simply look the same in Mp3tag). Some of those AAC encoded CDs with MP4-tags are just perfect, so cover art, album, title, artist and genre do display on the car's display. But most are simply "non-existent" to the car's entertainment system.

Is there a way to find out what's the difference between them (those which are recognized and those which are not) and - more importantly - how to fix this using Mp3tag?

Obviously I could re-encode everything as MP3 because the ID3 tags work fine - but I would like to avoid that if possible.

This is just wild guessing as over the distance it is very hard to tell what the difference might be:
The guess: could it be that you have stacked tags and one of them is empty?

To test this, create a column in MP3tag with the value "%_tag_read%[ (%_tag%)]" (it could be that such a column is already there).
This column should show "MP4"
Select a file that does not display properly.
Use the file list contect menu and Cut the tag.
If you have no stacked tags the column will go blank.
If you have stacked tags then you will still see "MP4" but no other tag data.
Delete this tag (and all further ones that might be stacked) and finally paste the tag again that you have cut initially.

Thank you for the suggestion, Ohrenkino. I tried. I kept removing tags for minutes. Still - that test-column still showed "MP4 (MP4)". After a while I made sure in the options that all tag types were checked for removal in those two tag-sections and continued removing for a while. Still - "MP4 (MP4)". Giving up on this. What's even weirder and makes me think that maybe the car's MMCS is buggy: some of the albums which displayed well before now don't anymore (ok - I copied them to a new SD-card but can't remember changing them). So maybe the problem is not with the tags but with the software of the Mitsubishi MMCS. Guess I'll have to convert all music to MP3 if I want the tags to be read correctly in that car.

There are scar-system which don't care about tags but use their own included database.