We have one of the clusters over which we see high heap usages around 80% levels over a couple of nodes. The cluster has around 10 nodes in total, but heap is seen high only on couple of nodes. All the nodes have a total RAM of 64G and heap set to 30G levels. The total shard count over these nodes is in between 700-750 shards, which lies within the recommended 25 shards per 1GB heap.
What could be the reasons for such high heap?