Are the boxes marked with the correct address? That’s the only way I can see misdelivering mail on a new or unfamiliar route. For a regular sub? They’re either running DPS to the street and not paying attention, miscasing mail in wrong slots and again, not paying attention, or lastly: they’re being told to hurry up to help another route and again, not paying attention.
Write it on the 4240- with # of misdelivered addresses. And ride management until it’s addressed.