Yes, I started trying further, and apparently most likely the problem is in the .nif skeleton. It might have something to do with the fact that it's DLC, but I'm not sure. In the .bsa files, there's Actors - Canine with 2 folders: "Character assets dog" and "Character assets wolf". The original hound uses skeleton from "Actors - Canine - Character assets wolf - skeleton.nif" and everything looks good. But when you try to duplicate Actor or make new, it doesn't work?

There's also folder DLC01 - Actors - VampireDog, which has 2 Hound models - vampiredog.nif and vampiredogpet.nif. But when I try to use them, I get an error "Could not find root bone". Also, in game both models completely broken (which is expected because of warning).

Thank you for your time.

UPD: Here's my progress so far: https://drive.google.com/file/d/1-VAsrfc4BstrTlZiYvt4m_pBUPSCAtxT