All entries have the same id

If multiple atom:entry elements with the same atom:id value appear in an Atom Feed Document, they must represent the same entry.

Ensure that every distinct entry has a distinct id, and ensure that every unique entry only appears in a given feed exactly once.

If the atom:entry elements in question represent the same entry, perhaps at different points in time, be aware that the potential exists that different consumers will display different subsets. If this is not a concern, then no action is necessary.