Tracks are not showing on my SanDisk USB Ultra 3.0 when exported through Rekordbox

About 1/3 of my tracks are not showing on the memory stick (SanDisk USB Ultra 3.0) in Rekordbox or using my XDJ-700s, but do show when I click on finder (I have a Macbook Pro) when I click on the USB in there. It doesn't really make any sense as most of them are MP3 and bought from Bandcamp. I can share one of my export logs if needed. This is really annoying as they're fully synced and play through Rekordbox, but just don't appear on my memory stick once exported. I've tried sync manager as well as manually clicking export on playlists and individual tracks. Could this be a problem with the USB itself? It's formatted as an MS-DOS (FAT32). Thanks