I have noticed a "bug" with short songs. Not just songs, any audio file in general, that is less than 30-40 sec. (haven't tested that).
The conversion fails at the end of the sample, essentially not removing the vocals from the song, kinda weird.

Here's a recent sample I did, but I noticed that this has been happening for a long time https://wetransfer.com/downloads/b5e...5100341/2e003b