Hmm, true, but would you expect them to be able to lock up the whole system?

Anyway, I spoke too early. Shortly after my post everything locked up again. But the reset to factory default still did something to increase the period until freeze-up to 3 days instead of 1-1.5 hours.
Intuitively, I would say that speak against a hardware failure.

I will keep observing it for a while to see if it happens regularly again and report back.