I had two problems with my bluetooth controllers, maybe the information is helpful for you.
The first problem was that I wasn't able to pair anything. This could be resolved by disabling bluetooth ertm mode. To do this, add
controllers.bluetooth.ertm=0
to recalbox.conf and reboot.
The second one was that one of my SF30 pro lost connection after some restarts in regular intervals, so I had to remove all controllers and repeat pairing all of them. This problem vanished when I removed and paired the controller from the command line. Also, a keyboard that would refuse to pair from the GUI could be made working by pairing via command line. I don't know the reason, but you might want to give it a try.