1.6.4 can produce compute errors on BC drivers, maybe you have a ton of those? That is why i recommend 18.3.4 or18.6.1 on the first page, it works a lot better on those drivers. Maybe if you can try it on one of those?
I have rather old rig with 4 polaris cards (8gb) and win 8.1. There are no recent amd drivers for win 8.1 so I'm still using August blockchain ones. And when I try to switch to bittube v2 and srbminer 1.6.4 I've got severe share drop (effective hashrate measures for 1 day 3.2 khs. miner still shows good hashrate on its console window, ~4khs)
So I had to switch back to heavy and 1.6.0 version ((
Don't wanna install win10 on this ancient rig ....