I've just set up my second rig with 8 vega 56's. I am using xmr-stak-amd. When I go to global wattman, my gpu frequency can only go to -4% or -8% for some. I am using the Aug 23 blockchain driver. When I open xmr-stak-amd and let it run, the hashrate stays at 0 h/s. Eventually it will show 1500 h/s for all 16 threads. I'm not sure whats going on. Any suggestion or help is appreciated!
Try to DDU and reinstall the driver from scratch. Better, avoid using Wattman to UV or OC, try to use OverdriveNTool.
Have you try to disable & enable all Vega on PC reboot everytime? It should get you to 1.5-6k hash each card with 2 threads intensity; Do remember to OC your mem clock to 900 - 950 Mhz to achieve higher hashrate (for stock 56 BIOS), or 1000 - 1100 Mhz (flashed to 64 BIOS).