For information, with the following configuration:
recalboxOS 9.1-Pulstar
RPi4b 8Gb
16Gb SanDisk SD Card
1Tb USB3 SSD (initialized mode "Move share")
8bitdo SF30 Pro pad (v1.34 latest firmware)
I was able to reproduce @Valippo explained issue.
I was also able to fix it following procedure:
Launch Bluetooth sync procedure from both Recalbox pad menu and SF30 Pro pad sync button
Bluetooth sync SF30 Pro pad successfully
Disconnect any other pad (Virtual pad or other bluetooth sync pad) from Recalbox
Launch buttons configuration with freshly SF30 Pro sync pad (now input are working and recognized)
Hope it helps 😉