On the newest server, I have replaced the motherboard (was unstable and would only lock an i9-10900x at 4.0Ghz).  Replacing the motherboard got that up to 4.3Ghz but did not fix the stability issue AND introduced a new issue, this new motherboard has two dead DIMMS slots and it appears to be a compatibility issue as many other users with Corsair memory have experienced the same problem.

Replacing the i9-10900x with an i9-10980xe CPU brought the stable clock speed up to 4.8Ghz (with 18 cores) and instead of the additional cores making it run hotter, it actually runs about 30C cooler under full load than the i9-10980xe does.  So everything is good except the dead memory slots.

I’ve ordered another motherboard, this one from Gigabyte because Asus customer service has not been helpful.  I plan to put the machine back into service with 192GB of RAM while awaiting the delivery of the new motherboard next Wednesday, so it will go into service and then go out again for motherboard replacement.