It's not new. They filed suit over a year ago. They threatened to withhold federal money and our governor and ( then ) AG told them to pound sand. Their lawsuit is flawed. They clearly didn't read or don't understand the SAPA. They are suing on the grounds that federal law trumps state law, but SAPA doesn't attempt to override federal law. It simply makes it illegal for state officials or LEO to enforce federal law. If it isn't a state law, we won't enforce it. Hence, bump stock bans, brace rules, ghost guns, red flag laws, etc. will not be enforced by Missouri and we will not cooperate with feds who enforce it.
It's also worth pointing out that if they were successful in overturning it on those grounds, a million lawyers and attorney's general would immediately file suit in every state where pot is legal and immigration sanctuary cities exist.