Maybe our cluster become unreacheable or with high latency.
I personally believe that tasks cancellation can be help to decrease load in cluster ?
I try this :
GET /_cat/thread_pool/search?v&h=node_name,name,active,rejected,completed GET _tasks?actions=*search&cancellable=true
At the end, i search to retrieve all search task cancellable to cancellation during high load in cluster.
Thanks for help.