I added a new test index (5 shards and 1 replica)
Adding the image of head:

![Screenshot%20from%202019-04-15%2019-28-39|162x500](upload://bhIY6nvs2tpOxNqN407LSFr4AOD.png)

I can see this error from  _cluster/allocation/explain

      "decider" : "throttling",
      "decision" : "THROTTLE",
      "explanation" : "reached the limit of incoming shard recoveries [6], cluster setting [cluster.routing.allocation.node_concurrent_incoming_recoveries=2] (can also be set via [cluster.routing.allocation.node_concurrent_recoveries])"
    }

It's not trying to allocate on old nodes. I tried to increase the above value, after that the replica shards also allocated only to new nodes with status "yellow."

---