I've got this weird problem with stale shares rate for quite a while. 5-7% of stales to be precise (up to 10% on a 180Mhs 6 GPU rig at a time). At first I thought it might have something to do with GPU firmware, or process priorities, or claymore (been trying different versions, keep installing the latest with no improvement whatsoever). Tried to get rigs work through proxy, but then it became obvious that direct stratum is fastest way anyway. Network issues are out of question - I run gigabit switches to the router, then to the fiber optic router, and get 79ms to the ethermine pool. CPU load on rigs generally around 2-5%, and I use raisers v.006c (quite standard stuff). Here's my screen https://imgur.com/a/Xf8IDeM

Any suggestions?