Restoring a single shard from backup with other unaffected shards requires a number of special considerations and practices. This document outlines the additional tasks you must perform when restoring a single shard.
Consider the following resources on backups in general as well as backup and restoration of sharded clusters specifically:
Always restore sharded clusters as a whole. When you restore a single shard, keep in mind that the balancer process might have moved chunks to or from this shard since the last backup. If that’s the case, you must manually move those chunks, as described in this procedure.