That makes perfect sense to me. I have suspected the perfect pass, but didn't have mine on when it happened so I discounted it. But maybe you don't have to have it on for it to affect it. (Guardian mode is the computer stepping in and shutting everything down to about 2000 or less rpm/s. Won't let you go any faster-to protect the engine I suppose in case of overheating or low oil pressure).
Haven't heard that about the deleting codes but that makes sense too. I have also suspected either a water pump or thermostat that is about to fail or at least the sensor thinks so, but discounted that because the dealer said it wasn't throwing out a code. Every time the guardian mode kicks in the first thing I do is look at the temp guage. It spikes to 170, then comes back down to 160 after a couple of seconds. Like yours the guardian mode goes away by just turning the key off and back on. Sometimes it might be another week before it does it again. But just need to get to the bottom of it so I'll stop pissing off skiers by suddenly stopping!