I was just about to use the bridge test model and Simplify3D decided, that the part that should be fully bridged will actually just have both sides bridged and the rest infilled
from what i have noticed is that it will bridge the outer perimeters then try to do short and not full extrusion strands to connect the 2 walls. they usually end up as very fine little strings and not a full normal infill. i could be wrong with this but i have seen it in the past and it does have an interesting way of bridging but it works.