Could not delete reference in specific level sequence

Could not delete reference in specific level sequence.

It seems to be a soft reference because it becomes a reference for pink color, but I do not know where it is being referred.

1. Create new Level sequence and level.
2. Spawn Cube to the level.
3. Bind cube to level sequence.
4. Convert to Spawnable on cube.
5. Convert to  Possessable on cube.
   At this time, BindPossessableObject is executed twice.
6. Delete cube.
   At this time, UnbindPossessableObjects is executed once.
7. A reference is left when trying to delete the New Map