Given you’re on a new board now, i’d RMA the CPU.
In Windows:
Open Task Manager and look for “System Interrupt”
It’s a catchall for something going wrong. It will lock the whole system up if there are PCIe issues under any kind of load. I’m in agreement on bad CPU or it might be that you’re pushing too much through too few PCIe lanes and the chip is having trouble speaking to everything, lots of small stutters leading to a lock. Had this problem in a few mining rigs - was always a bad PCIe riser, fried card, or i mucked up the CPU install a pinch (i hate the fingers in the 7th gen intel socket).