I"ve noticed the same problems with the B-3X IOS module. It seems to be stable as long as you don"t do any app switching. Once you start switching between it and even only one other running app, the B-3X will sometimes become totally unresponsive to both local and MIDI commands. The only remedy is to kill and restart the B-3X. I"m running it on an iPad mini 6 under iOS 15.2 with only one other app running (SongBook +).
I"ve opened a case with the vendor but so far haven"t received any response.