film it and report it. Its a bug. The absolute thinnest armor on the turret is 150mm on the gun mantle, and even then its assuming they didn't just slap it on over the turret armor, and instead modeled the small area of overlap, and the gun mantle armor alone for the rest.
Panzer IV's maximum armor penetration is 136mm at 0yds, 0 degrees slope, at sea level.
Anything with a gun weaker than the Tiger I shouldn't be able to penetrate the Tiger II's frontal armor at any range.