Some Structures Don't Generate when using the Locate Command

If you create a floating island world and do /locate a structure, it tells you the location of the structure.  However, if you teleport to that location, it is completely empty.  This is for ruined portals.

 

World Type: Floating Islands;  Biome: Plains

Generate Structures: On

Bonus Chest: Off

Seed: 3329

Coordinates from /locate: -126.5 57 -148.5

Ruined Portal: -512 ~ -304