By usability problem I mean that some users are saying their cities appear in the list but they can't calculate routes. As shown in my post just above I'm able to get information from Hamburg and Milan (I haven't been there ever, that information comes from the app).

See post #22. "Covered regions" are those cities fully supported with timetables. Then there is a bunch of cities (including Hamburg and Milan) with transport information but no timetables.