Highly likely your CPU is faulty, this is a known issue. My first 5900x was faulty and then the replacement they sent me was faulty as well. 3rd one seems to be okay. Same-ish symptoms, mine would reboot while playing certain games in certain zones. I could run stress tests fine, but certain games/zones would trigger it and after 1-2 reboots would be fine for awhile. Only had it reboot 1 time in a stress test.
It could be your memory, whea19 is usually a memory or infinity fabric thing where whea 18 is usually processor cores, so try each stick alone in the proper slot.
While you're testing your memory use CPU-Z to see what your CPU stepping is. There are 2 steppings,B0 and B2 with 2 being the latest. The belief is that the 0 stepping has more stability issues and the B2, since it is a more refined process, has less. The B2 is also rumored to use less power and because of that potentially boost higher as well. If yours is a B0 stepping and the memory isn't the culprit then it's the CPU, RMA it.
