Freestyle render, Hidden lines showing, Error?

Why are the lines pointed to by red arrows showing? They are the outer edges of the cube that is the room. The room is one object, a cube, with a solidify modifier for wall thickness (and openings cutout with boolean subtract modifier.
Applying the modifier doesn’t help. Strangely some of the outer lines show (erroneously) and others don’t. There are other problems with hidden lines too, if for example I extend the kneewall behind the toilets beyond the room confinement, to intersect, I will sometimes see a line at the edge of that wall, outside the room… (and a known limitation freestyle will not generate a line at the intersection of the two objects)

Below is the same shot without the crease lines (no problem with those hidden lines… but not enough lines to outline the room)

Below is an Eevee render