There is nothing crazy, everything is where it should be. However after running MP3Gain, it has stored the gain tags as APE values. All of your other tags are in the id3 format tags. You can see this indicated in the top bar of your first screenshot in post #1.
There are plenty of other threads here with suggestions for handling this issue with MP3Gain.
https://community.mp3tag.de/search?q=Mp3gain%20ape%20order%3Alatest