i7-7800X constant freezes on ubuntu, what could be?

Question

ubuntu

CPU i7-7800X, ubuntu 18.04 / 16.04
Very often hangs tightly, the mouse moves a little, but only a hard reset helps.
Most often it happens under high load, when all the cores are involved, for example, when I compile the code.
It may just freeze in the browser, but this is much less common.
The memory is ok, memtest passes, I even tried different vidyuhi, but it does not help.
It was ubuntu 16.04, updated to 18.04 and the same thing.
Still stood Windows once, there such a problem has never been observed.
I will be glad for any help.