This new build 1803 of Windows has been nothing but problems.
The proper built to mine is 1703.
1709 has many PCI problems, and yes 1803 others including (some say) decrease of hashrate...
You may better install 1703. But also check swap file; I usually reserve 8GB per card, to be safe. Some miners crash with less.
My Vegas' hash rate dropped from 1900 to 1400 H/s on build 1803 and as far as I can tell everything else was the same as it was, configuration-wise. Reverted to the previous build and the hash rate went back up. I'm really curious what is going on with build 1803. Was using the August blockchain drivers, maybe it's a problem there. I've never had luck with the Adrenaline drivers.
EDIT: It appears many people are having a lot of problems with 1803, especially with AMD cards.