Certain MP3's won't import to Spotify at all

[glman]

So, I have a mixtape i downloaded years ago off of an artist's website. It's in my music folder, it's extracted, it's in the .mp3 file format. For some reason, the songs from that mixtape will not show up under "Local Files". All of my other music does, but never those songs.

What's weirder is, on my old laptop, they all appeared and I synced them to my old iPhone. For some reason, they won't import on either my desktop or laptop and I have run out of ideas. Anyone have any suggestions?

(Running Windows 10, on a new Dell laptop)