I wasn't too sure whether it's related to the missing vertex bug or not (that sometimes your vertex dot didn't display, therefor you cant select vertex even though you're on vertex sub-object mode), but you can try to convert it to mesh then back to poly, at least it fix the missing vertex bug for me.
Hey y'all, I'm having this issue where sometimes my 3ds max viewport becomes really inaccurate, and it's being an absolute pain! (attached image) The vertex + wireframe starts to look slightly offset from the shaded model, and when trying to select individual vertices the actual vertex slection "area" is offset (pink dot)…