All good advice here.
But it may well be the CPU. Rad game Tools officially documented the same problem for Alder as Raptor. In the case of Alder the blame is squarely put on the mainboards for aggressive clocks and voltages. Yours may be degraded now.
Having seen so many reports of Zen 2 degradation, for my money, aggressive settings being the culprit tracks. Combine it with the silicon lottery, workload, passage of time, various other factors, and you have some CPUs failing under the conditions where others do not.
If it stabilizes when using really conservative CPU and ram settings, it is almost certainly degraded.