At Manchester Airport (Lancashire, UK) all of my terminal buildings are offset. At Heathrow [EGLL] and other airports they are not. I do not have any addon scenery installed at all of my knowledge, but I do have the PMDG 777-200LR/F package and FSpassengers installed.
I've tried installing custom scenery to fix the issue, but some gates are still inside the buildings and others are too far away etc. Any help would be greatly appreciated!
Be sure that everything you added (plus the aircraft) are all made for Steam.
Check your scenery folder eg world scenery for EGCC Bgl files you have two scenery Bgl files conflicting.