Hello everyone!
I also have 2 GPU Vega 56 and when I add the -G 0,1 line everything crashes and I have to restart.
Otherwise using only one card i get 1950h/s, even 2000 if i put power usage to 0%.
It crashes even if use WinMiner and a very low power setting on Wattman.
I am afraid that the PC crashes using 2 gpu, because the motherboard may not be strong enough it is a 3 years old Gygabite, maybe is not recent enough. It is supposed to support 2 AMD Gaming GPU (even in crossfire) though...
On a different note, For those who gets Hs drops after a while it may be because the fan are below 3000rpm.
Pretty much as I stated above...
it is not the mobo, I followed step-by step to setup my rig
http://vega.miningguides.com/ I have 2 Vega 64 on a 5 years old Asus P8H61-M LE and i get stable 1960 H/s per card, your problem is the Wattman.. quote from the site: "If you installed the full AMD application, NEVER EVER open the AMD application. In other guides you will hear references to Wattman. Ignore them. You will hear references to HBCC sliders. Ignore them. Opening the driver software works for some people but I have had to uninstall and re-install the drivers ground up because of opening the driver. Don't do it. You need it installed and that is it. (If you did open it and have problems that require uninstall"
I use wattman with no problems. Day after day of stability at over 2K average hash rate on 4 vega 64's. It's not Wattman that is the problem, but I concede that it of course is far from perfect.
Make sure you have 8MB of Virtual Mem per card set in your virtual mem space (windows10). 1024 * 16 for (2 cards) = 16384 + 300 for overhead =16684 total. OR maybe better settings 2 (cards) 1024 *16 *1.5 = 24576VM.
Make sure crossfire is turned off (should not be an option if using the blockchain driver so generally ignore people saying this)
If using wattman sometimes it is best to toggle the HBCC on off after PC reboot. (leave it off on all cards)
My fans are set to 2500RPM min with a target 70C and max of 75C - You will need to adjust fan speed per your climate.If you can keep the cards at 70C and lower, all the better.
turn the monitor settings in windows to never turn off.
That is about all really.
Fire up the script and let it run. You can turn your monitor off and on and the hash rate should stay the same.