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PC reboots with RAM working at 4000Mhz

Level 7
I have some issue and I'm curious if anyone experienced something like me.

I have 8 pieces of Corsair 4000Mhz RAM - 8GB each (64GB together). When they run at 4000Mhz speed the PC reboots after several seconds of Prime95 CPU stress. When I change the memory frequency to 3800Mhz, the CPU stress can work for an hour and no reboot occurs.

Now what is strange: when I put 4 memory sticks into 4 slots on the right side of the CPU - they can run at 4000Mhz without any problems. When I put the same 4 memory sticks on the four memory slots on the left side of the CPU - the PC reboots on CPU stress (only at 4000Mhz). I want to emphasize that it is not about corrupted memory, because I switched memory sticks - the same sticks works on the right side, but they don't work (i.e. reboots) on the left side.

What is more important and strange - I have my PC for almost one year (I bought the mainboard on a premiere). I have many issues on the start like freezing and reboots, but I've managed to resolve them (by updating BIOS and changing the power supply). My PC was working perfectly for about 6 months with all memory set to 4000Mhz.

When I changed memory frequency from 4000Mhz to 38000Mhz I thought that I solved the problem, but the PC then started to freeze at completely random moments and under no CPU stress (for example when I was doing nothing in Windows). Moreover - I can stress the CPU with Prime95 and no freezes or restarts. I changed the memory frequency to 3000Mhz and I thought that this solved the problem, but the PC has frozen once again, but this time after 3 weeks (it was freezing much more often at 3800Mhz).

I don't know if the freezing and rebooting are problems arising from the same source. I remember that after I noticed reboots at 4000Mhz I've also updated the BIOS to 1401, so maybe the reboots problems were connected with memory speed, but the freezes are connected with new BIOS version. I think that because I had freezes just when I bought the mainboard and the BIOS update solved that problem. So maybe the problem has returned in 1401 BIOS.

Full spec of my rig:

BIOS: 1401
CPU: Intel Core i9-7900X @ 3.30GHz (LGA 2066 R4)
Memory: Corsair CMK64GX4M8X4000C19 (Module Size 8192MB)
GPU: Asus Strix NVIDIA GeForce GTX 1080 Ti

Level 7
You can think at a memory controller not at its best in the cpu or a not good contact on the cpu socket.
Try to remove your cpu and look at socket pins with a magnifier lens. Every pin has to be vertical and not bent. Clean the contact side of the cpu and reseat.
If nothing changes, you can try to modify advanced parameters of memory in the BIOS.