Unexpected higher total ops [7] compared to expected [6]

Elastic Stack Elasticsearch
1

I'm getting the below error from time to time and every time, the master node Goes down due to the below error,

[2024-09-24T15:39:12,682][ERROR][o.e.b.ElasticsearchUncaughtExceptionHandler] [xxx-xxx-xxxx-elasticsearch-master-1] fatal error in thread [elasticsearch[xxx-xxxx-xxxx-elasticsearch-master-1][search][T#2]], exiting
java.lang.AssertionError: unexpected higher total ops [7] compared to expected [6]
        at org.elasticsearch.action.search.AbstractSearchAsyncAction.onShardFailure(AbstractSearchAsyncAction.java:403) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.search.AbstractSearchAsyncAction.lambda$performPhaseOnShard$2(AbstractSearchAsyncAction.java:270) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.search.AbstractSearchAsyncAction$2.doRun(AbstractSearchAsyncAction.java:303) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.common.util.concurrent.TimedRunnable.doRun(TimedRunnable.java:44) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:737) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37) ~[elasticsearch-7.10.0.jar:7.10.0]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130) ~[?:?]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630) ~[?:?]
        at java.lang.Thread.run(Thread.java:832) [?:?]
Caused by: org.elasticsearch.action.search.SearchPhaseExecutionException: Shard failures
        ... 10 more
Caused by: org.elasticsearch.tasks.TaskCancelledException: The parent task was cancelled, shouldn't start any child tasks
        at org.elasticsearch.tasks.TaskManager$CancellableTaskHolder.registerChildNode(TaskManager.java:522) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.tasks.TaskManager.registerChildNode(TaskManager.java:213) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.transport.TransportService.sendRequest(TransportService.java:629) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.transport.TransportService.sendChildRequest(TransportService.java:712) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.transport.TransportService.sendChildRequest(TransportService.java:704) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.search.SearchTransportService.sendExecuteQuery(SearchTransportService.java:139) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.search.SearchQueryThenFetchAsyncAction.executePhaseOnShard(SearchQueryThenFetchAsyncAction.java:83) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.search.AbstractSearchAsyncAction.lambda$performPhaseOnShard$3(AbstractSearchAsyncAction.java:244) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.search.AbstractSearchAsyncAction.performPhaseOnShard(AbstractSearchAsyncAction.java:279) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.search.AbstractSearchAsyncAction.onShardFailure(AbstractSearchAsyncAction.java:406) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.search.AbstractSearchAsyncAction.access$100(AbstractSearchAsyncAction.java:70) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.search.AbstractSearchAsyncAction$1.onFailure(AbstractSearchAsyncAction.java:258) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.search.SearchExecutionStatsCollector.onFailure(SearchExecutionStatsCollector.java:73) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.ActionListenerResponseHandler.handleException(ActionListenerResponseHandler.java:59) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.action.search.SearchTransportService$ConnectionCountingHandler.handleException(SearchTransportService.java:408) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.transport.TransportService.sendRequest(TransportService.java:670) ~[elasticsearch-7.10.0.jar:7.10.0]
2

You are running a very old version that is EOL so I would recommend you upgrade to at least version 7.17 to see if that resolves the issue.

[EDIT] This seems to be reported in this issue and appear to have been fixed in version 7.11, so my recommendation to upgrade to 7.17 should resolve this.