The BBC has seen video of the crowd that formed in Milan Bergamo, showing frustrated passengers telling staff they’d been waiting at the gate for more than an hour, asking “What do we do?” and saying that information was “too slow”.
EES requires non-EU citizens, including Britons, to register biometric information, including face scans and fingerprints, which can then be checked each time they cross a European Schengen Area border.
It has been phased in since October and was meant to become fully operational on 10 April.
However, its introduction has been more successful in some parts of Europe than others.
Ryanair said: “Due to passport control delays at Milan Bergamo Airport on 16 April, a number of passengers missed this flight from Milan to Manchester.”
According to one passenger, about 30 people were left stranded. Ryanair did not say how many travellers were affected.
Milan Bergamo Airport has been contacted for comment.
EES is run by the relevant border control authority in each country rather than by the airport or airline.