While adding thermal paste to the cpu's for analytics1040, a piece of the dried and flaky paste came off and landed inside the pins of the cpu slot. I thought I was able to get it all out but it turns out a piece remained and during inspection, it is now crushed inside the pins.
To be sure I swapped the DIMM from A to B and no change l
I swapped cpu's and no change leaving only the system board.
The server is under warranty so I will create a ticket with Dell.