19.11.3 solved it; 20.2.2 didn't work.

Vega 56: Hynix - 23.7, Samsung - 24.3 MH/s
Core 1100/815mV
Mem 915/810mV
0% power limit
Timing level 1 in OverdriveNTool
480W from the wall
~50 deg C at ~55% fan speed