Just picked my car up from the dealer. They included a copy of the manufacturer’s instructions to technicians. It’s a known software issue, and they believe it is related to CarPlay. Once they’ve fixed the problem a notice will go out to PP owners recommending we come to the dealer for a software update.
In the meantime, when it happens you can either disconnect the battery, or pull the “Radio/USB” fuse. The latter is easier; the fuse box is on the passenger side of the engine compartment. There is a diagram of the fuse box inside the lid (pay attention to the arrow signifying which way is front). It’s the 15 amp fuse closest to the driver.
I think I’m going to buy a cheap USB keyboard and keep it handy. With my luck this will happen again while I’m wearing a suit and it’s 105 outside.