@Tomberry Nothing faulty here, just how the CPU works.
Totally normal behaviour for Ryzen cpus, you can see it from your readings too.
When your cpu is mostly idle, then it puts most of the cores to sleep, and runs 1-2 cores really fast, at 1.4V, and that means those 2 cores are quite hot, because I mean, 1.4V, but the total power the CPU draws is low, so it can afford to deal with that heat output.
But when you stress test, then the CPU can't run all the cores at 1.4V, that would be madness, so the voltage quickly drops to 1.2V, and all the cores are at that voltage, so much less heat in a few hotspots, so the cooler can more effectively deal with the heat.
When you stop the stress test, most of the cores go back to sleep, and the cpu can run the remaining cores at higher voltages again.
So nothing to worry about.
You just need a better fan curve, that doesn't spin the fans up until a higher temp. Much harder alternative would be to use PBO with negative curve offset, so the voltage never goes that high.