I have used mp3tag on Windows before the switch to Mac and have tagged my audiobooks for use with audiobookshelf. There was a discussion about which tag to use for book series (as far as I have found, it should be GRP1) and audiobookshelf changes its way to include GRP1 in the scanner (see https://github.com/advplyr/audiobookshelf/issues/3681).
However, I tag the files with Yate (I have checked "Maximum Grouping-Work Name compatibility) and while the files appear to be correctly tagged (verified with kid3, GRP1 tag with e.g. "Harry Potter #01" in UTF16 encoding), audiobookshelf does not pick up the grouping.
This does not happen when using mp3tag, despite the tags being the same as far as I can tell.

Any ideas what could cause this?