They could challenge the procedural validity of the Amendment, especially one created via a Constitutional Convention. Which is what I was referring to. It may be a stretch but it is possible and if the Supreme Court took it up and ruled it unconstitutional then what recourse is there. Given the state of the Supreme Court, I would not put it past them either.
The recourse is to have the states say, “the Supreme Court has no jurisdiction in this matter, so its opinion isn’t binding.” And then to convene the convention whether or not Congress agrees.