IN does not work, it is stored as a serialized array. IN only works when a meta field is stored in multiple DB entries. LIKE must be used for serialized arrays.
Are all the selected posts in the relationship published?
If that’s not it then the only thing I can think of is that the value of get_the_ID() where it is called is not the post ID you think it is. Is this in any type of a nested post loop?
