I drew a “rectangle” of which the 4 endpoints turned out to be non-coplanar. Of course, the “face” didn’t fill up. Fair enough.

But then, to resolve the problem, I drew a diagonal in the rectangle, to form two triangles. Each of the triangle SHOULD form a face and fill up, because there ALWAYS exists a plane that connects 3 points. Well, one of the triangles doesn’t fill up (?!)

Interestingly, when I further subdivide the triangle that didn’t fill up into two triangles, again only one fills up. The problem persists as the triangles get smaller, and smaller, and smaller …

Weird

Please anyone advise.