From my understanding of sync/append design, an under construction block should not have any block locations associated with it in the blocksMap. So an under construction block will not be managed by ReplicationMonitor.
However, if there is an error in the write pipeline, a lease recovery will trigger a call, commitBlockSynchronization, to NN. This call will add the successfully-recovered datanodes to blocksMap. This seems to violate the design. It should update the targets of the last block at INode instead.