Just updated to 5.3.4
All the problem cases are fixed, awesome! 
However it triggered some error which I’ve made another topic for:
(With its own reproduction project attached)
Which while I was looking to understand what caused it, accidentally found a case that still managed to create a new area from a navmesh! D:
However it seemed very unlikely to happen, and is in a particularly weird case of using a very big max step height (7m)!
This is doesn’t happen when making the navmesh cuts taller so the navmesh doesn’t enter from above or below, but only the sides.
This case doesn’t affect us much with how rare it seems to be, plus this high max step recast graph was an experiment so we can get rid of it. No rush here.