My HP z840 doesn’t use my 2nd CPU

So to start off with what some basic info and what I have already checked or done:

• ⁠Z840 Workstation • ⁠1125W PSU • ⁠2129 Motherboard • ⁠Windows 10 Pro • ⁠2x8 Samsung DDR4-2400 • ⁠2x8 Samsung DDR4-2133 • ⁠2x Intel E5-2678 v3 (12 cores 24 processors) • ⁠CPU’s are seated correctly • ⁠Power to both CPU’s are correctly fitted • ⁠RAM-sticks are seated in the correct slots • ⁠BIOS is on the newest update • ⁠Cleared CMOS • ⁠Installed all possible drivers for this CPU/CPU’s generation from Intel, Windows and HP • ⁠BIOS detects both CPU’s, the total 48 processors, and benchmarked both of them • ⁠MSconfig, TaskManager, CPUz, OpenHardwareMonitor and Intel Processor Diagnostics only detecs 24 processors and shows 1 CPU detected

This isn’t something that occured after something changed in the PC. I bought the PC from a friend this has always been like this.

Only thing I can think of is that the 2133 and 2400 RAM’s dont work with eachother in a way that they can support a 2nd CPU? But with the way they are seated, my guess is that that would also cause a problem in the only processor working. And the only thing I haven’t tried is switching the CPU’s places and seeing if it’s a socket problem or a CPU problem. But since the BIOS flawlessly benchmarked all 48 processors, I don’t suspect that the problem lies with the CPU’s or the sockets. My final solution would be to bring it to a PC shop, but before I try that I want to see if I can find the solution myself.

If I am wrong in anything please tell me! And if anyone can tell me something that I haven’t checked or done to see if there is more to try, also please advise me. Thank you!