neither my -400 or -400F show leading edge device panels when flaps are extended.
The underside support structure extends, but no panels are attached to them.
Looking at the texture.cfg file in the baseline "texture" folder there is a line "fallback.3 =..\texture.f"
However, I see no such folder that this is referred to.
My -400F has the same problem because there are texture fallbacks to the -400, which obviously causes the problem again.