I’m facing a similar issue, but unfortunately on iOS there is NO workaround that I can find. Either Apple or Line 6 should man-up and let us select if the audio interface is active or not! A simple menu item to turn off the interface, just like we can with MIDI would be fantastic. As it is now, I will have to buy a bunch of adapters to use MIDI via DIN cable so I can leave the USB cable unplugged. Lame