When a nss.rename(otherNss, dropTarget) command gets executed on a sharded target collection, every shard participating in the DDL is currently adding an internal {op: drop} event to its oplog when the target collection gets locally dropped.

This may generate some ambiguity from the perspective of a mongos serving a otherNss.watch() request (which is collecting oplog events from multiple shards) to establish the exact point in time at which the change stream may be considered as invalidated.

To solve this, non-primary shards participating in the rename collection DDL should mark their oplog events with the fromMigrate attribute.