Hi Aydin:
The 17pdr gun is not like other AT guns in game. This one is a force modding. In vanilla game there is not a movable 17pdr, we force the model inside the pit to work as movable unit. That why this particular unit looks and act a little funny.
My advice to you with it:
If you lose the gun and the crew survive, then try to use an ambulance to recover the gun. You can buy the death soldiers and the gun will appear again.
Sadly we have limitation with the tool and we need to adapt to have more models in game.
Regards, Olhausen