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 ....
Windows 10 is better and quicker than Windows 8.1. You must update 8.1 to 10.
Polaris cards with 8Gb allready old and even ancient?....