There are certain cases (direct shard connections, refineCollectionShardKey, etc.) that can cause a shard which does not contain any chunks for a sharded collection to not have the correct shard key index for the collection. This is generally fine (we do not expect these shards to have accurate indexes), but if that shard has pending range deletion tasks the range deletions will not be able to make progress without the shard key index.

This can cause issues with balancing where no chunks can be moved back to the shard in question.

It would be nice to be able to find shards where this is the case via checkMetadataConsistency.