I had the same problem on my Rallye Redline. I was heading to College listening to music on a USB, switched songs and BOOM. The sound went off, radio screen froze, all the like. I did what you tried and stopped, cut off the engine, and open the door- still was on. In the end due to the rain and the fact that I had about an hour and a half till class I took it to the local dealer to get it looked at ( dealership was on my way to class). The radio turned off randomly while I was waiting for a technician to check it. Yesterday I was driving around and again the radio stopped twice, but each time it came back on. I'm not an expert on any of the electronics in our cars, but to me that looks like some sort of bug in the software. The stealership said theres no update for the radio but I don't believe that. FYI I got a Uconnect 730n in mine, hopefully yours straitens itself out, still wondering what it was that caused it.
