On the phone, any firmware constantly flies or goes into reboot. What is the reason?

Question

Android

Samsung GT-i9082, I don’t know how it works with the official 4.2, but on custom it sometimes goes into reboot, but it doesn’t crash. But the CM12 and the other fly off, for unknown reasons. It was during the installation of applications from the Play Market ...
This time I thought I was lucky, I decided to install CM12 again, I took it seriously, everything was as it should, according to the instructions, in order, everything was done perfectly, and the same crap ... Is it really a hardware problem? And what exactly?
I've flashed the official 4.2, then the recovery, then through the CM12 recovery, then the gaps, and you're done. (I didn’t forget about wipes, the instructions say when and what wipe to do).

Answer 1

Reboot - looks like overheating or broken memory.
Firmware corruption - flash memory is corrupted.
Or maybe it's bad soldering (microcracks).
That's just with the official firmware and you need to check. All these "customs" are raw by definition and are not considered for stability tests!