Other mistake: During the hill climb up terrain shaped like a valley with rocks on either side, a soldier is directly hit with a large explosive, probably from the big guns, and his severed head lands down on another soldier's back, who is crouching to help another man. When the head lands on his back, it is just an empty helmet, but when he looks at it on the ground, you see the partially alive, severed head lying next to it with much of the neck still attached.
Other mistake: In one of the air battles, the one where our heroes come to aid to a platoon of infantry harassed by German Fokker D.I's, the plane of Lowry is under fire after he downed an enemy airplane. In one shot, you can see he gets multiple hits just behind the pilot seat. Since these planes are barely armoured, say not at all, Lowry should have been punctured by the bullets at his back as well, instead of being completely fine. (01:16:00)