I have reinstalled the app so all my settings are freshly default and I have done a full scan. Still have the same issues, but here are my findings and observations:
For FLAC, in PA, artists can be stored in multiple, separate ARTIST tags. Artists are shown in PA as separated with "; " (semicolon and space), so they are shown as "artist1; artist2". Although the multiple ARTIST tags are recognized and separated with a "; ", for some reason they are not split by default due to the underline going underneath the entire tag. Therefore, using default settings, multiple artists are not working. However, a workaround exists by adding ";" to the "Symbols to Split Multiple Artists" setting. After adding that, "artist1; artist2" are properly split into 2 separate artists shown by 2 underlines, one beneath each artist name. If this is intentionally done to support multiple artists in such a roundabout way, then ";" should be included in "Symbols to Split Multiple Artists" as the default setting.
For MP3, in PA, null characters become replaced with a " " (space), so if an ARTIST tag was artist1<null>artist2 (or artist1\\artist2 in mp3tag for example), PA shows it as "artist1 artist2" and the multiple artists are not split due to the underline going underneath the entire tag. There will be no way to get this to work using the "Symbols to Split Multiple Artists" feature properly if any artist names include a space.
It seems using the above findings, we can determine that at least for PA build 933, null characters for multiple artists are not supported for MP3 files only. It seems like the null characters in MP3 files are intended to be replaced by "; " so that the "Symbols to Split Multiple Artists" feature can split the artists with ";", but this is currently not the case.
If null characters were supported properly for MP3 files and working in previous builds, then a regression in the source code probably occurred.
Semicolon ";" should be included in "Symbols to Split Multiple Artists" as the default setting due to the way current support for multiple artists work.
Attached pics below show how this works for FLAC files with default settings and then with ";" added to "Symbols to Split Multiple Artists".