Weird rebalancing strategy

7.3.1
Yes. I have increased the node and task counts like below.

PUT _cluster/settings
{
  "persistent":{
    "cluster.routing.allocation.node_concurrent_recoveries":10,
    "cluster.routing.allocation.cluster_concurrent_rebalance":60
  }
}

I make similar changes whenever I add new nodes to speed up the rebalancing. This is the first time I've seen such behavior where new nodes will never reach the shard count as others. The shard count on those new nodes just fluctuate up and down and I noticed one new node being on both the source and destination. It seems a wasted move.
This is the first time we have increased the data node size to 25. With 21 data nodes and below, I have never seen this on the same version of ES (7.3.1)