One thing i have noticed is setting too aggressive Negative Curve Optimiser it causes exactly this problem, either that's what he has done or the CPU he has is too aggressively tuned out of the box, IE the CPU might not be a bin at the quality its tuned for, setting a Positive 2 Curve Optimiser should fix it but honestly its one that probably should just be sent back.
As for Idle power, Zen 3 Cores idle at an incredibly low idle power, mine idles at about 0.02 to 0.03 Watts per core, that in its self can cause issues, its so low it can make the OS think its shut down which would cause it to shut off.
mobo vdrop and vdroop can affect it too