Title does not explain your question to enable full comprehension, at least for me. But I'll give it a try...
I don't recall any "reset"; just some achievements that didn't make sense anymore were moved to feats of strengths (i.e., achievements that can't be completed anymore in RoS). I have no idea what you mean by "achievement reset", though.
That is probably a result of the difficulty change. You didn't kill them on torment, you killed them on inferno or whatever.
To be fair, some of those achieves could have been harder when they were first done than they are now. Personally I think they should have just gave us the updated achieves I've we had the equivalent already. Was pretty depressing to see achieve points drop and know you had to do them all over again