14900K with Asus Maximus Z790 Hero ever increasing instability

[Cuscaden]

Bought an Intel 14900K, an Asus Maximum Z790 Hero and Corsair Vengeance DDR5 2x32GB 6600 RAM. Built the system on April 25th, all went smoothly, transferred over my 4090 and two WD850+ SSDs. System powered up and booted up on the 1st attempt.

I updated the bios to version 2202 and applied the Intel defaults. System was rock solid until Saturday morning when it started crashing. Read up and manually applied 253w/125w/308A power limits as recommended by other people seeking stability. Seemed fine for a few days, then Discord would crash every time I tried to open it, reinstalled it kept on crashing. Removed the windows store version and downloaded it from the Discord website, and it seemed fine. The Ubisoft Connect app would start crashing. MPV started crashing with app crashes and exception in the Windows Application Event Viewer, OTOH I could run something like Far Cry 6 for hours without any problem.

This Saturday I decided maybe I needed to have a fresh windows installation, so set about doing that, created the windows install USB on another PC, started install and I was getting a mixture of different stop exception errors, 0xc000021a repeatedly and sometimes a system service exception and a few other random blue screens.

Turned off XMP, ran mem test and got a clear bill of health on the memory.

Reseated memory, re-did thermal paste on CPU (H150i XT Pro with the 1700 screws), but try what I may I cannot get this system to install windows, boot off the USB stick, it copies data over, reboots, and then 0xc000021a in the same place each time.

I replaced the SSD with an older version which was my OS drive a few months ago, boots up fine. Grabbed a different SSD that I was happy to format, went into Windows install, removed all partitions to allow Windows to do what it wanted to the drive and started getting errors saying it could not format the drive. Rebooted, this time it moved forward, and then on booting the system failed with a "system thread exception not handled". A fresh install OS is impossible on two different SSDs. The system is "stable" in the bios and in memtest. It would seem reading data is fine, but as soon as you go for writing data errors begin to crop in.

Just contacted Amazon and have started a return for the CPU since that is relatively easy to return and swap out. 

Any ideas what could be going wrong? Thanks.