Can't find supported files when using Local Files

[SketchBook]

Country

America 

Device

Desktop/PC

Operating System

Windows 10

My Question or Issue

I'm trying to add and find local files to a playlist of mine. I know how local files work, and I've gotten it to work before. But the thing is I had some files which I added to the local files. Tested to see if they would work, and they did! Downlowed to the playlist and everything. So I removed them from the playlist to give them a proper name. But when I changed the name of the file they stopped working. I cannot find them or anything. I tried making a new folder, adding the mp3 files to it, but then the new folders I made wouldn't show up either. Please, if you know how to fix the problem then tell me. I'm willing to try an explain better if you need more information.