If we have this sequence on the donor:
1. createCollection foo
2. createIndex unique index {x: 1} on foo
3. dropIndex
4. insert some documents to foo that violate uniqueness on x
------
After cloning, the recipient could clone documents in foo without index idx. And in the tenant oplog application phase, the tenant oplog applier would apply 2. and fail this invariant because during tenant oplog application we relax constraints.