Perhaps a Motherboard VRM is reaching a high temperature and causing a brief drop in load as clocks are throttled.
with all of the cores loaded, probably the CPU throttling back to cool down to prevent self destruction
all multi-core processors can only handle so much TDP before they overheat
1 of 1 people found this helpful
I would agree with amdmatt in that it is most likely an overheating VRM, considering how "naked" that board is. Doubt it's temperature related given how high Ryzen can tolerate temps.
Compare it with the ASUS ROG STRIX B350-F which has quite a bit more heatsink on the VRMs