Vega 64 throttles it's memory clock in games sometimes.
So for some strange reason, the memory clock would be stuck in a really low clock like 167 mhz after running for a while, temperate of HBM2 usually hovers around 80-83, anyone knows why? This seem to occur after the new driver updates that included the auto undervolt/clock/memory feature ..
Setting/Unsetting "HBCC Memory Segment" and applying seems to fix the issue without requiring a restart. It's not really a solution but it can save you 5 minutes.