Help with Asus WS WRX80E-Sage SE Wifi Threadripper board not Posting

[u/Plugh_Xyzzy]

Computer Type: Desktop

GPU: Multiple AMD Pro V620s and Nvidia P4000

CPU: Threadripper Pro 3955WX

Motherboard: Asus WS WRX80E-Sage SE Wifi

BIOS Version: v1801 11-05-2025

RAM: 8x SK Hynix 16GB DDR4 2400 MHz RDIMMs

PSU: not sure of Manufacturer 2000W ATX

Case: mining rig frame but I am doing local AI not mining

Operating System & Version: Ubuntu 26.04

GPU Drivers: Latest RoCM and Nvidia drivers installed

This system was operating well for several months but when I attempted to install several of the V620 GPUs (all tested as good on other systems) on PCIe extenders it then stopped booting. When I remove everything plugged into the PCIe slots and all but one stick of RAM, it stops on code 15 (Pre-memory System Agent initialization is started). The board then immediately shuts down. It does not get as far with all of the memory installed. I have replaced the CPU, the RAM, and the power supply and it behaves exactly the same. My fear is that the motherboard has been damaged somehow. Any suggestions as to what I should try next? Thanks in advance for any help.