Legal Question in Constitutional Law in Louisiana

Yes. In fact, even without a motion, if the court realizes it lacks subject matter jurisdiction, the case must be dismissed. See FRCP 12(h)(3): "Lack of Subject-Matter Jurisdiction. If the court determines at any time that it lacks subject-matter jurisdiction, the court must dismiss the action."

https://www.law.cornell.edu/rules/frcp/rule_12

Yes. That is at least the general rule. It's always true in federal courts. It's true in the state courts here in California, too. There might be rare, narrow exceptions in the laws of some states, where a party can waive particular types of subject-matter defects in cases that are based on the state's own laws. But I doubt it.

Your question is posted under Louisiana law. For historical reasons, Louisiana's laws sometimes work quite differently from federal law and the laws of other states. I'm not licensed in Louisiana, so don't rely on my interpretation. But I just did some very quick research, and it looks like the general rule applies in that state's courts as well.

If this might be an issue in a real case, please speak with a local attorney about the specifics. She may be able to help you find a solution. Better yet, she might tell you this really isn't an issue in your case at all.

Good luck.