Not sure where to start with this one. Been searching everywhere I could; websites, forums, discord, etc. but I keep coming up with no answer.

I recently installed 4x 8GB ECC more sticks into my R510 which gives me a total of 8x 8GB. However, when I install the RAM into the A4 & B4 slot, the server randomly hard shuts down. No errors or warnings. 

The sticks are 8GB, ECC and registered, RDIMM, 1333Mhz. 32GB is Samsung, 32GB is Hynix (other than brand, they are completely identical)

Have done memory testing on A1-A3/B1-B3 with sticks installed and diagnostic comes back passing. It crashes when I try to do tests with RAM in A4/B4.

Is the mobo dying, or the CPU... or is there some other tests I can perform? CPU issue? 

 

Much appreciated for any tips or if someone has come across this before and has an answer.