In brief, Ingram's EPUB verifier does not permit the "belongs to collection" property.

I've been discussing this with them for well over a year. They say that they are working on resolving it. (Of course, they said that a year ago, but I hold out hope.) For the moment, I make a special Ingram version of each EPUB for submission to them - exactly the same, except for deleting this property.
I use Sigil for book prep, and it's quite easy to delete the property from its metadata manager.