I have the exact same issue... driving me crazy... i tried so many different solution and scenario... I tried to reinstall all mods related to skeleton and animation mainly XPMSE and FNIS. Tried the steam integrety check. Tried running LOOT (no issue found) SSEedit auto cleaned what needed to be cleaned. probably missing a tons of other things i've tried lol Still haven't found what causing this. If anyone solved it, please let us know what mod caused it and how you fixed it. thanks