CPU 2 need second riser. C34RV is the part number of second riser. Can you remove riser and check the behavior. I believe R450 with 2 CPU will work without risers also.
I added a second processor to the R450 server purchased with one Xeon Silver 4314 processor. An error is displayed after startup:HWC8010 The System Configuration Check operation resulted in the following issue: Config Missing: Riser 2. Is it possible to start the system without Riser 2 so that the error does not appear? I don't need a PCI device (in Riser 1 and Riser 2). If I configure the server in the Dell shop, it is also possible to select the "No PCIe Riser" option. I assume that the possibility of starting without Riser 2 is possible.
PE R450 without Risers