I've been having a strange issue where certain MP3 files are refusing to be detected by Spotify. Even while still in a folder with other files that are currently being detected, they are considered missing whenever Spotify is re-opened. It's almost like they are untoggled.
Just as a follow-up, I've tried reinstalling Spotify, deleting and recreating the folder I'm pulling the files from, and changing the drive that the files are on. None of these have solved the problem whatsoever.