It seems to have been extra problematic the past couple days. It's returning flights that don't exist as if they do (search LHR-JFK and it'll return VS 25, which doesn't go to JFK, but DL.com says it does). Also, even more frustratingly, trying to book a trip with multiple travelers, the top tile where you enter the pax info is supposed to automatically populate the same fields in the secure flight info tile, where the name field is grayed out so you can't enter that info manually. It was not doing that and I had to keep refreshing the page until it would. Grrr!