Bug - Weird stance : with rapier and estoc weapon

Platform:
Geforce Now

Do you have any mods?
Nothing

Please explain the issue is in as much detail as possible:
When a character use a rapier or an estoc weapon he makes a weird battle stance with an arm lift up and the body completely straight. I am definitively sure that this is not suppose to happen.

The hand holding the weapon stands upright, The other hand is lifted like a bare hand. I think each is programmed separately. And i don’t think upright is the right stance.

Please tell me how to solve it or how to avoid it.
This will always happen. is not it?