Black Spot on mesh while using DFAO

I’m working with a modular building kit where the inside and outside of the walls are separate pieces (both one sided). The outer wall (in mesh editor below) curves around the inner wall.

When I enabled DFAO I got a big black spot on the inner wall. My guess is this has something to do with the outer one sided wall curving around the inner wall. I was able to “fix” the problem by enabling two-sided distance field generation in the mesh editor build settings for the outer wall, but honestly I have no idea why this works. I also tried changing the outer walls distance field resolution scale to no avail (and it had the downside of using more memory for the distance field).

What exactly is causing this problem?

two-sided distance field generation is the correct fix
by default distance fields assume that the mesh is a closed solid, so everything inside it gets a zero distance (aka. black in DFAO). by using the two-sided flag you tell it to behave like a shell so it also generates the distance field towards the inside