1. The new zone range can conflict with the old zone range. If a user reshards from a hashed shard key to the same shard key but unhashed, there could be extraneous conflicting documents in the config.tags collection. This could cause issues with the balancer.
^This will cause the old zone range and new zone range to both still exist post-resharding. We don't delete the previous zones because the hashed and unhashed shard key have the same shard key shape.
2. If the zone ranges are the same for the new and old shard key, we will see a duplicate key error like