I just passed through this experience with my i7 8700k.
Its overclocked a lot to 5GHz all cores AVX offset set to zero, DDR4 OC from 3 to 3.6GHz, lots of voltage tweaking.
The OC was very stable and then I need Virtualization, turned that thing on via BIOS, then boom, 10 to 15 min of gaming the PC freezes. I reboot, play again, same crash after some time. And I know when is CPU/RAM issue because it just freeze, GPU freeze gives you a random color at the screen when freezing (my GPU too is heavily OCed lol).
So, after a lot of tweaking my voltages I could never get back to my previous overclock. Remembered that I changed that Virtualization setting, turned it off, and BOOM, all things are perfect stable on the previous voltage settings.
It does something to the CPU, what I don't know, but surely makes it more vulnerable to crashing when heavily OCed.