Please note that the only valid representation in MP3tag to show the MP3 field TPE3 is ALBUMARTIST.
You could check the Options>Mapping whether you have mapped any "album artist" to ALBUMARTIST.
If not, then all the non-ALBUMARTIST fields are user-defined fields.
The best way would be to copy the contents of the existing fields to ALBUMARTIST and delete all the others.
The case, BTW, of the fieldnames usually does not matter.
But if you want to do that: