Originally posted by yucafrita
Dont forget cameras today are computers. As such, just expect they might crash.
I've had my K1-ii for a few months now and it has done that a few times, though to me it happened during pixel shift shots and some times just in live view without shooting any picture. A couple of the times I had to leave the camera without battery for several minutes for it to recover as just removing it and reinserting after a few seconds wouldn't bring it to life. It would just make a loud click sound the first time the switch is turned on and then nothing happens.
Whether by coincidence or not I noticed that each time it did it I was using a rather old third party battery which I had bought for the K3 many years ago. I think this is in line with what Adam said about voltage dips.
I have since stopped using that battery on the K1-ii and haven't seen the problem again. Curiously that same battery still works fine on my K3, perhaps it is less demanding on the battery.