Unfortunately, I ran into the same problem tonight.
I edited the preset through HX Edit. I had two lines - on one volume pedal, a looper and a large reverb, on the other - several delays and big reverbs.
I wanted to switch the speed of one of the delays using a foot switch. Then a similar story happened - all the buttons froze, the sound disappeared, and nothing changed after the reboot.
What saved me - after the reboot, the first 2 milliseconds hx effects reacts normally, and MIRACULOUSLY in these 2 seconds I managed to copy another preset to the dangerous preset location. The processor freezes in the "data transfer" status, but after a reboot it turned out that he had rewritten it.
I really hope that Line6 will fix this problem, as it turned out, there are a lot of people with such a problem, and this is unacceptable for an expensive device that is positioned as for concerts.