I have this same symptom, what was the fix for yours @invidiaboy?
I have tried rebooting and a firmware update and it's still happening. It's possible my attempt to factory reset failed but it's hard to tell due to having no usable screen.
The device still seems to work. I can play through it and switch presets via the rack. I can also control it via the controller. Just the screen is messed up.
For me the problem occurred on first boot up, although my unit was a replacement for my previous faulty rack and the staff at the store had tested it, so I'm not sure what they did before giving it to me.
