It's possible that in some configurations of aphantasia the brain is still doing some sort of processing that is made available via a subconscious process.
So you can't visualize an occluded surface in an active way but your brain still prevents you from running your rear bumper into another car.
Many people with aphantasia still dream at night.
Congenital aphantasia and emergent aphantasia may effect brain structures differently, perhaps some forms just disconnect the pipeline that feeds the brains computed data back into our visual centers for further visual analysis.
It's very interesting, in running down these differences we would probably learn a lot about the brain.