I've had this problem with the large rocket prop before.
I contacted other members of this board and they don't seem to have a clue.
Have you tried to replicate this issue with other similar props? Have you deleted the issue prop and tried again? Or, can you move the prop to another location of the map (for instance, in the middle of an open area) and then see if it works correctly?
Otherwise, I would suggest deleting that prop and restructure the awning section of the building. Maybe make the awning for only one side of the building, not both sides.