Plex does not support the Part Of Compilation (TCMP) tag for MP3 files unfortunately, so the scanning agent has to rely on various fuzzy criteria to identify various artists compilations, which as you’d expect is a hit and miss affair.
It’s been a source of much frustration for years and by now the devs should know that adding support for Part Of Compilation is how to fix it, it’s just not high on the priorities list.
