When dragging a list of 50 mp3 files in to the app, only 33 are added, the rest needing to be added manually. The order appears random, but it is the same tracks each time, and can't drag the rest of the tracks in without over writing the others.

Right as I posted this I realised the issue. All of the songs not uploading, had special characters [In my case brackets, indicating featured artists.] Which must be invalid characters.