A find by UUID can return NamespaceNotFound without taking any database lock. This allows a reader to see intermediate state from an operation that has the database locked in X mode and is performing catalog operations that may be rolled back. This is problematic for the rollbackViaRefetch algorithm, where a NamespaceNotFound error is treated as a promise that the collection will be dropped in a future oplog entry. This can lead to inconsistent data between replica set members.