NavMesh not quite joining from stairs to next floor, Why?

I’m not quite sure why my NavMesh breaks on my penultimate step?
The top step manages to generate a height map properly but not the one just before?
Why is this happening, how do i fix this?

I have found a fix.

Seems that the banister mesh was interfering with the stair mesh. Making the banister “walkable” as daft as it sounds fixes the issues of the mesh not joining properly.

Imagine it’s the wall underneath the problematic stair that is confusing it?