MP4 Files that won't Tag (or the amazing incredible invisible tags)

I have been enjoying tagging my MP4 collection of files using MP3tag and it has been a tremendous help.

However I don't know what to do about files that will not accept tags. Out of many 1000s of files there are over 100 that will go through the motions of tagging but the result is blank. The files are from different sources that are not connected.

Have others encountered this and do they have any remedy or tools to investigate the issue?

Perhaps your problem has something to do with this thread: