I've used keyfinder to find a key of a particular track. When I load this track into pioneer RecordBox the key field shows up with the information that was detected in the keyfinder however when I load the same track into mp3tag the initialkey is empty. I think there is the same issue with BPM field
Mp3tag stacks tags with priority APE>ID3v2>ID3v1.
The APE tag hides the other tags.
Deactivate the reading of the APE tag in Mp3tag options and look into the ID3v2.4 tag whether the missing data is stored there.
Then come back and ask for more.