Many people have asked this question but nobody has answered properly. Ok, some of the pages returned to their high positions on Firefox on 2 different sites. Tests performed logged out of Google account! Positions changed yesterday and stayed fixed till now but the strange thing, no traffic! Check your positions on different browsers if you see any difference. If it's Data center related, i felt a little hope for recovery. If it's not, Google shows my favorite pages higher in SERPs when i am not signed in.