Problem 1: While using a series of simple walls stitched together using the “Form Extended Structures” flag, the following behaviour occurs:
Navmesh is no longer generated on the object (deal breaker here), and the previous generation appears to have been offset, this occurrence is 100% reproducible in my tests. Complex and simple joined DMs.
Problem 2: In a worse scenario: when combined with “World Support” to prevent the entire structure from moving while applying force on it, walls will retain Navmesh occlusion. This behaviour does not occur when the “Wold Support” flag is off, or set to True without “Form Extended Structures”.