You should therefore ask him to clarify which it is, and if he thinks it is an official rule, you might ask him to show you the rule. I don’t think there’s a lot of merit to that particular change it doesn’t affect that many spells (and there are much more powerful spells than mass lesser vigor that you can still persist under this rule), but that is his call. If he’s saying that he’s making such a houserule, then that’s his prerogative as DM. Note that Persist Spell explicitly changes the Duration of a spell, and therefore that maximum is no longer in force. That rule does not exist, and mass lesser vigor is definitely persistable. If the claim is that there is an official rule that prevents you from persisting things with a maximum duration, he is incorrect.
