Server Version#: 1.28.2.6151
Player Version#: 1.53.1.3225-c0bc6cc4
Until a few months ago my music library showed multiple genres using local metadata, but now only shows the first in line. I tag the files using Mp3tag (ID3v2.3) and use \\ as a separator between genres.
For example, Melodic Death Metal\\Death Metal would show as two distinct genres and I could sort and play by either genre. A semicolon does work, but am not interested in retagging almost 2TB of mp3s.
There was a regression in Plex when they switched to a new tag scanning library (ffmpeg), multivalued tags in id3v2.4 (and mp4/aac) are indeed not picked up anymore.
However, a patch has recently been submitted in ffmpeg that will fix it, so as soon as that’s accepted, it will cascade down to Plex.