About this image

Finch Farm overpass navmeshed with accessible stairs. The vanilla navmesh for the overpass was incomplete, only part of it was navmeshed, and what was navmeshed was about 3 feet under the actual road, so that might have been why settlers would fall through it when coming towards Finch Farm from a distance.

If I can make sure it doesn't cause any issues in game, I'll upload it as a mod.