Hi,
I'm struggling with the same issue as described here. Unplugged the headphone jack cable while playing a sequence and the MF froze. Trying to reboot it resulted in it getting stuck in the booting screen. I managed to connect it to my computer and have it recognized by the midi control app. It now reproducibly boots again but only outputs a constant wave which changes in pitch and amplitude as soon as the display changes. This sound plays even though no key is pressed, nor the hold button or a sequence is activated. This constant sound only appears when MF is connected to my computer. When MF is receiving power only via the power cord, it just outputs a click sound when the present is changed. I also tried different headphones and stuff, it's the same with all of them. I tried updating the firmware and also using older firmware but nothing solved the issue. Same with the misc settings reset on the device itself.
Did anyone of you find a solution??