I have same exact problem, I bought my unit new when they first came out and it has been barely used since then, I can usually get passed the update flash error if I plug in a guitar cord but it still acts flaky and then does same exact thing next time I plug power in. I can see that firmware is updated to latest version and I tried rolling back firmware and then reinstalling latest firmware on my mac instead of PC windows 10 PC with a different USB cable with no change in update firmware error. I have never had a product that cost $500 new fail in this way.