This was a cooperation between me and Michael Stembera: -me recognizing SF having problems with resolving FH's efficiently at high depths, thus starting some tests based on consecutive FH's. -mstembera picking up the idea with first success at STC & LTC (so full credits to him!) -me suggesting how to resolve the issues pinpointed by S.G on PR #1768 and finally restricting the logic to the main thread so that it don't regresses at multi-thread.