Pressing any switch should exit the tuner mode. Can you try it with MIDI cables (instead of wireless) and see if the issue persists? And put the MC6 on an independent MIDI Channel as well.
@james I’m having the same issue with my MC6pro, but with a Kemper powered head. Using cables, midi output to kemper channel 16, input from kemper channel 15. I can get the kemper to go into tuner mode and the MC6pro to display the tuner but if I press any button on the MC6pro it freezes, Kemper does not exit tuner mode and displays a notice that the midi device has been disconnected. Only way I’ve been able to get the MC6 back to normal after this is to reboot it. Controller is running firmware v3.11.2. Any advice is much appreciated!