Fast Track for SK@ARN yesterday also had some very slow families with young kids who got directed to what was usually an empty and fast moving Fast Track checkpoint. But what really was slowing it up was some teenage girls who just took their jolly old time to gather their stuff and clear the bins.
At least historically, CPH Express and OSL both seem to have some people directed to the express screening at times even when otherwise not entitled to use the express screening arrangement. CPH way more for me than eVen OSL and also more than various other Schengen airports.