So I've noticed differing levels of performance in the way the H9 control iOS app and the H9 interact when receiving midi signals (in my case from my computer via ableton). Sometimes the interaction is perfect: I open up a midi clip in ableton, start moving around an automation line that's assigned to a CC that's mapped to a parameter knob on the H9 and all 3 move in concert – the CC in the midi clip, the H9's display of that parameter, and the parameter in H9 control on my iPad.
Sometimes it's far from it. for example right now I have two simple midi clips playing successively, separated by 1 bar – one to engage the pedal, one to bypass. With H9 control open and connected on my ipad, the H9 won't bypass when i play these clips. But if I close the app, it works fine. I've found over the months this can sometimes be a pattern. I'm having difficulty getting midi to work on something I'm programming and then i close the control app and everything works fine. This leads me to conclude that the bluetooth connection is somehow causing an issue.
The Bluetooth connection is sending the same sort of control signals (in functional terms) as the MIDI. So, if you have both active, they may fight each other to some extent. To make them work at all together, we have had to make MIDI lock out Bluetooth and vice-versa so they don't interrupt each other in mid-message.
It is likely that this lockout process can be improved. The way the unit was conceived, it was that people would use BT for editing, and MIDI for performing. As we are leaning, the reality is much more complex.