So I finally managed to import my playlists after some hassle, but now my playlists are all titled with .m3u8 and I cannot seem to get rid of them. Is there a way to remove them?
They are file-based lists now, so they will end in M3U or M3U8 (in the same way that MP3 filenames end in MP3).
What you could do is to long-press on one of those playlist filenames in Library>Playlist and select 'Add to Playlist'. Then create a new list name, and PA will add the entire contents of the physical M3U file into a new internal playlist. Then you can move the original file copy away to some backup location that isn't set for PA to scan.