I’ve been trying to reproduce your problem, but I haven’t been able to. So, you’re activating the tuner on the H9 itself by pressing the two footswitches, and then when you exit the tuner, H9 Control crashes? What screen are you in on H9 Control when this happens?
I’m just using H9 Control to activate the tuner by selcting the pedal icon then selecting the tuner. While tuning, the app randomly crashes going to the ipad home screen. At the home screen, I’ve noticed the tuner on the pedal is still active and responds as expected.