There seems to be something in front of the door and elsewhere along the wall causing the navmesh to be pushed back. What is causing that? You could also try lowering the Agent radius to see if you can get it to connect, but there seems to be something else going on.
You could also try lowering the cell size to have tighter corners.
Is your navmesh dynamic? If you wan to change what’s blocked and whatnot, it should be dynamic.