Popped up in Serverless. When resolving, let's mention internal issue ES-13155.
"Failed to execute phase [fetch],
at org.elasticsearch.server@9.2.0/org.elasticsearch.action.search.AbstractSearchAsyncAction.onPhaseFailure(AbstractSearchAsyncAction.java:624)
at org.elasticsearch.server@9.2.0/org.elasticsearch.action.search.SearchQueryThenFetchAsyncAction.onPhaseFailure(SearchQueryThenFetchAsyncAction.java:81)
at org.elasticsearch.server@9.2.0/org.elasticsearch.action.search.FetchSearchPhase$1.onFailure(FetchSearchPhase.java:88)
at org.elasticsearch.server@9.2.0/org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:29)
at org.elasticsearch.server@9.2.0/org.elasticsearch.common.util.concurrent.TimedRunnable.doRun(TimedRunnable.java:35)
at org.elasticsearch.server@9.2.0/org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:1067)
at org.elasticsearch.server@9.2.0/org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:27)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614)
at java.base/java.lang.Thread.run(Thread.java:1474)
Caused by: java.lang.ClassCastException: class org.elasticsearch.search.aggregations.bucket.nested.InternalReverseNested cannot be cast to class org.elasticsearch.search.aggregations.InternalMultiBucketAggregation (org.elasticsearch.search.aggregations.bucket.nested.InternalReverseNested and org.elasticsearch.search.aggregations.InternalMultiBucketAggregation are in module org.elasticsearch.server@9.2.0 of loader 'app')
at org.elasticsearch.aggs@9.2.0/org.elasticsearch.aggregations.pipeline.BucketSelectorPipelineAggregator.reduce(BucketSelectorPipelineAggregator.java:48)
at org.elasticsearch.server@9.2.0/org.elasticsearch.search.aggregations.InternalAggregation.reducePipelines(InternalAggregation.java:119)
at org.elasticsearch.server@9.2.0/org.elasticsearch.search.aggregations.bucket.InternalSingleBucketAggregation.reducePipelines(InternalSingleBucketAggregation.java:142)
at org.elasticsearch.server@9.2.0/org.elasticsearch.search.aggregations.bucket.InternalSingleBucketAggregation.reducePipelines(InternalSingleBucketAggregation.java:137)
at org.elasticsearch.server@9.2.0/org.elasticsearch.search.aggregations.InternalAggregations.lambda$maybeExecuteFinalReduce$0(InternalAggregations.java:197)
at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:214)
at java.base/java.util.Collections$2.tryAdvance(Collections.java:5182)
at java.base/java.util.Collections$2.forEachRemaining(Collections.java:5190)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:570)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:560)
at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:265)
at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:723)
at org.elasticsearch.server@9.2.0/org.elasticsearch.search.aggregations.InternalAggregations.maybeExecuteFinalReduce(InternalAggregations.java:198)
at org.elasticsearch.server@9.2.0/org.elasticsearch.search.aggregations.InternalAggregations.topLevelReduce(InternalAggregations.java:187)
at org.elasticsearch.server@9.2.0/org.elasticsearch.action.search.QueryPhaseResultConsumer.aggregate(QueryPhaseResultConsumer.java:423)
at org.elasticsearch.server@9.2.0/org.elasticsearch.action.search.QueryPhaseResultConsumer.reduce(QueryPhaseResultConsumer.java:255)
at org.elasticsearch.server@9.2.0/org.elasticsearch.action.search.FetchSearchPhase.innerRun(FetchSearchPhase.java:96)
at org.elasticsearch.server@9.2.0/org.elasticsearch.action.search.FetchSearchPhase$1.doRun(FetchSearchPhase.java:83)
at org.elasticsearch.server@9.2.0/org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:27)
... 6 more
"
Popped up in Serverless. When resolving, let's mention internal issue ES-13155.