The MigrationChunkClonerSourceLegacy code has several invariants to ensure that no document operations are lost during chunk migrations. One is to ensure that no operation is done after the critical section and the other is to ensure that all updates have been transferred to the recipient shard.

Both these invariants assume that all updates are getting blocked while the shard is in a critical section. However, this is not the case for broadcast multi-update and multi-delete which do not contain shard version.