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


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."