The case of the day is Department of Human Services v. M.C.-C. (Or. Ct. App. 2015). The Oregon Department of Human Services brought a dependency proceeding against a father who lived in Mexico but whose four children lived in Oregon. The DHS served process via a private courier that required a signature at delivery. This service failed to comply with the Hague Service Convention. However, the father appeared in the case and actively litigated it for two years before raising the defense of insufficient service of process.
The ordinary rule is that you have to raise the defense of insufficient service in your first pleading, and otherwise you waive it. The question in the case was whether anything in the Convention required a different outcome. The clear answer in the cases is “no,” and so the court denied the father’s motion.
I don’t believe the Practical Handbook addresses the question, but it seems to me that on general principles the law of the forum will determine whether any particular argument has been waived. This seems particularly so given the non-mandatory nature of the Convention. So I think the outcome is correct.