Remember to stick to ID3v2.3 for MP3 tagging to stay 100% compatible. ID3v2.4 is less popular, and often implemented worse. Such is life with informal standards…
mp3tag is still pretty good, FYI. But if you use a good media player/library, a dedicated tagger is rarely necessary.
(My guess is Music Match, RIP, caused some grief with your MP3 tags.)