I've noticed these red vertices, the geometry seems ok, nothing duplicated or crossed.
It just baffles me, thinking something might be in error.
Any ideas?
Those are because you have some Creasing on those Vertices:
You can set it to zero (on selected Vertices, it will say ' Mean Vertex Crease when you have more than one Vertex selected) in the N-Panel, or use CTRL+V.
It is a relatively new feature, meant for use in combination with a Subdivision Surface Modifier:
