I'm about to tear my hair out. I have been fighting with these damn VEGAs all weekend!
After nearly a dozen hours I have a single Vega card working in my board.
Fresh install of Fall Creative Update
Aug 23rd Blockchain Drivers
XMR CAST 0.6
HBM: 990MHz
Mining XMR at 1,400h/s
Does anyone have any ideas why I'm so low?
In device manager disable and enable cards one by one.
Tried that repeatedly..

Maybe it was just coincidence, but I had a 1300 hash rate at one point until I upped virtual memory to 32GB.
This is possible. Current community understanding is that you should have 16GB Virtual Memory for each Vega. I made the mistake of getting 32GB of physical RAM, and I'm only using 10% (more if I have other programs running like HWinfo64) - never more than 8GB so far.
So I just ran out and grabbing 16GB of physical RAM (up from 4GB) and now I'm getting 1 running steady at 2000+. Holy cow 16 per VEGA? I think I set like 40 at the moment for 2 but I'll check. Now I'm on trying to get the second one to work..