Originally Posted by
Marambio
Wonder if it’s got to do with the Italian passenger locator form, although that wouldn’t explain why they can’t issue the boarding pass for the return flight.
Nothing to do with that, don't worry. It's just another (useful) system not or poorly integrated with existing checkin system, no communication between the systems and so they want you to stop at the counter to show your vaccine certificate even if you already sent it to ready-to-fly.