B-52H back gunner not working in Ground Realistic Battles

The B-52H back gunner is not working properly in Ground Realistic Battles.

I cannot access the back gunner at all, and it does not fire even when enemy aircraft are nearby. It behaves like it is just decorative, not functional.

In Air Realistic Battles, there is no issue the back gunner works normally. However, in Ground Battles, I am unable to use the 20mm rear gun in any situation.