The shard collection command makes a best-effort attempt to inform the primary shard that the collection is now sharded, but that message is not required to be delivered. This means that the primary shard owning the previously unsharded collection may not know that the collection is now sharded, even after it is.

We should test that if we get into a situation like that we can still establish a changeStream through a mongos that does know that the collection is sharded.