There are several reasons that this can happen
- There was a bug in versions prior to 1.30 that stopped ADE finding all the stock buildings and objects at an airport when the runways were running in a North-South direction. This has now been fixed so you need to be running 1.30 or later
- To see all the buildings and other objects in both ADE and FS you need to set the scenery complexity to Extremely Dense in both. Only at this level will everything be shown.
- You did not start from a stock airport or loaded an airport designed with another tool. Since different tools work differently we cannot be sure that ADE will handle everything the same way the other tool does.
- You have more than one custom version of the airport present and that airport file may be at a hight priority than the one created by ADE. ADE automatically excludes stock objects and taxi signs. It does not exclude custom objects or signs. If there is another file with a copy of the airport in it then the signs or objects from that file may be displayed by FS even though ADE have excluded all the objects and signs from the stock airport