I can't find anyone talking of this bug, so i'll just make a post here.
It only happens if i have a two handed weapon in my off hand and a one handed weapon in my main hand.
Basically if i jump off a horse while it is running (L3 press) and pull out my weapons, the off hand (heavy one) will have a bugged grip instead of keeping it on the shoulder as usual, and this fixes only if i go back on the horse and back down without making the horse run (L3 press).
I have made a clip and uploaded it on youtube, here it is: