Install FNIS to your Skyrim, Once installed - go to the skyrim folder, go to Data then tools then FNIS_for_users. Run "GenerateFNISForUsers.exe" and click Update FNIS Behaviour, once finished, exit and Skyrim's animations should be fixed. (it's used for mods with custom animations and required for those mods) I think it cleans and repairs general animations and combat animations and also, it looks like the owner of FNIS has already commented on this xD