When copying ID3 tag in mp3 from v2 to v1, or just changing tags and saving, Genre is not saved in ID3v1 at all, if more than 1 genre is used in ID3v2 tag (quite often now).
- genre: Pop/Rock
- year: 2020-01-01
- track: 01/10
- year: 2020
- track: 1
Conclusion, year and track is copied/saved to ID3v1 tag, but genre is not saved at all, so it's missing, it's a problem in some programs, which support only v1 tags.
Solution would be to copy the first genre to ID3v1 tag, if possible, at least as option, I think it's still better to have 1 genre (of 2 or 3) than no genre.
MP3TAG v3.04a, Windows 10 2004 64-bit.