I found a bug but adding a remote.invalidated check fixed it. perhaps we could be add a regression test to jstests/change_streams/report_post_batch_resume_token.js or jstests/change_streams/resume_after_invalidate_exception.js but the latter has some slightly different setup.
this test case needs to:

• watch a collection
• immediate save a pbrt
• drop the collection to invalidate
• watch the collection again starting after the pbrt we saved and filtering out all events
• then make sure the initial response and subsequent getMores have the pbrt

The point of this convoluted setup is to make sure that even when there are no events and an invalidation happens that the pbrt still gets set.