It seems like bandhelper was talking to the wrong device... That´s why I turned off WiFi.
I don't think I ever tested the MIDI functionality with wi-fi turned off. That shouldn't matter, but it might be confusing the MIDI engine somehow, so I would turn that back on.
Unlike with Midi-Commander, the LED on the Midi Interface does not blink when sending midi commands. Maybe my Midi commands or so bogus, the interface doesn´t accept them and so won´t blink it´s LEDs. But the midi learn features also doesnt´t receive anything, while it works fine with Midi-Commander.
But MIDI Commander is not installed now, right? I've found that that app is good at taking over the MIDI interface so other apps can't access it (only one app at a time can use a USB MIDI interface on Android).
Also, I wouldn't worry about the MIDI Learn now and just focus on sending MIDI. The reason is that those are two separate functions and it is easier to troubleshoot if you focus on one function at a time.
If you stop and restart the MIDI engine from the MIDI Status window, does that make Android prompt you to connect to the MIDI interface, and does the MIDI sending work after that?
Also, I didn't test this systematically, but I seem to remember that the connection works better if you do NOT select the "use this device by default" option in the USB connection dialog.