Did you finally find a solution?
I have the same problem with 8bitdo in bluetooth configuration.
I also configure it normally in ES.
If i use a usb retroflag snes controller, it works. strange.
@matze1980 Now it worked. The program i was using to convert the songs was making the bitrate bigger, due to my lack of attention. I put on a second song but now it just keeps playing and doesn't change to the first song i put on, why does this happen?