Originally posted by Łukasz:

I have observed a sometimes-occurring problem with my character shifting the weapon from one hand to the other while opening the door. You can see it well in the attached video link bellow. For example if my character is holding the weapon in his right hand, then after opening the door he starts holding it in his left hand. This looks unnatural and strange. This would make sense if the character could be two-handed. I thought maybe the problem is the "Swap It" mod? I must also add that this does not happen every time.

short video:
https://vimeo.com/898995662

This is caused by Fancy & Brutal Handiwork. The hotkey for swapping a weapon between primary and secondary is CTRL + E. I don't know if you're on console or something, but on PC Ctrl is also the alternative way of aiming - So if you're opening a door whilst doing that you will swap weapons. I'd suggest either aiming by holding down Right Mouse Button or rebinding Ctrl.
Tip: Whilst having two weapons equipped (or just one in your off hand), holding CTRL and attacking (LMB) will use your off hand instead. Doing so while unarmed will let you punch.

Thank you very much. I get used to CTRL as aiming so I had no idea that another mod uses this key. In the game options I changed the assignment.