Heart Issue #3 OCCT

Good evening, a few months ago I bought a processor with a second-hand motherboard, so far no issues, but after a while I wanted to change the motherboard because I couldn't overclock the CPU and run RAM higher than 2666 MHz. So I sold mine and bought another one, and the result was that it had bent pins. I wanted to return it but first I wanted to test it by straightening the 3 bent pins. So I did that and everything works except that when I launched a game, the PC crashed twice. Then I wanted to do a stress test with OCCT to see what's up with the CPU and I noticed after 1 minute "error on core #3." So I didn't want to dig deeper, I returned the motherboard and got another one. When I received the new one, everything worked; I was able to play games without crashing, but with some abnormal FPS drops (though maybe that has nothing to do with the CPU), and so I did a stress test with OCCT again and ended up with errors on core #3 again. So I tried putting the RAM sticks in one by one, switching them around, etc., I checked the voltages, temperature, and frequencies of core #3 compared to the others and everything seems fine, so I don't understand where these errors are coming from... I would really appreciate your help ????