This is strange. I was going to put together a model showing how I intersected the plan. I started by drawing a box around the plan as drawn(2d). I then move/copied the the plan/rectangle and intersected all faces. Surprise, it was fixed. This does not work on the original.
In my previous post I was referring to 3d block pulled up and down from the 2d rectangle. I selected all and intersected selected. This worked on the original plan but isn't required on the copy. I have no idea why, other than it may close some ends with vertical errors.
I'd be happy to learn something here myself if anyone knows what's going on.
Slightly confused
SS