Hi,
For me the default airport is loaded properly with 3D buildings, on default X-plane 11.05r2.
Confirm you can find the folder ...X-plane 11\Custom scenery\global airports?
That's where all the default 3D airport layout is saved.
Anyway, my advise would be to run again the installer to update x-plane. The missing or corrupted files would be downloaded again.
Best regards,
Guillaume