Same here, this behaviour happens when the Connection error shows up. I've had it for like 4 or 5 times now. Rather annoying, since the phone doesn't give any signal to show it has crashed and (I think) you can't receive any calls/text messages. Usually a power button long press did the thing, but of the 5 times it happened, I had to pull out the battery two times. Hopefully this bug will be fixed soon.