@Hellow: The default Black Ridge is only as good as the L9a. So only with VLP ram and a Noctua A12x15 you will get the max performance of the BlackRidge. My 3700x on the L9a has also some high peaks on some cores for some seconds ~65°C. You system isn't in idle all the time sometimes some windows process are running an the Ryzen will clock very high on some cores to handle these faster. Here are some Steps you can check:
1) What clocks and temps do you have while running Prime95 10minutes. Your Prime temps are ok but I need to check the cpu clock.
2) Please boot the system. Wait 10minutes and the monitor the temps with CoreTemp or Aida and post us the min, max and current temps.
3) Check the contact of the black ridge with the CPU. After disassembly you can see how good the pressure was. Maybe upload a picture of the thermal paste. Maybe your heatsink does not have good contact.
4) Install the newest Chipset driver and Bios updates. AMD made some improvements with the newest updates
5) Install the fan in suck in mode.
6) Make sure the fan does not work in silent mode
7) Don't use the I/O Shield
8) Reduce PowerPackageTracking to 80 in UEFI
9) If you use case fans they should push air outside the case.