I wasn't able to replicate (ran multiple times locally). But the error failure seems weird to me. It may be a strange race condition that isn't easily repeatable.

**Build scan:**
https://gradle-enterprise.elastic.co/s/qglznapknwmya/tests/:modules:reindex:test/org.elasticsearch.reindex.DeleteByQueryBasicTests/testDeleteByQueryOnReadOnlyAllowDeleteIndex

**Reproduction line:**
```
./gradlew ':modules:reindex:test' --tests "org.elasticsearch.reindex.DeleteByQueryBasicTests.testDeleteByQueryOnReadOnlyAllowDeleteIndex" -Dtests.seed=B36AB6B5F42DB7E5 -Dtests.locale=cs-CZ -Dtests.timezone=Etc/GMT-8 -Druntime.java=17 -Dtests.fips.enabled=true
```

**Applicable branches:**
8.10

**Reproduces locally?:**
No

**Failure history:**
https://gradle-enterprise.elastic.co/scans/tests?tests.container=org.elasticsearch.reindex.DeleteByQueryBasicTests&tests.test=testDeleteByQueryOnReadOnlyAllowDeleteIndex

**Failure excerpt:**
```
java.lang.AssertionError: 
Expected: updated matches <0L> and created matches <0L> and deleted matches <0L> and versionConflicts matches <0L> and failures size matches <26> and reason cancelled matches null and slices matches an empty collection
     but: was <BulkByScrollResponse[took=283.3ms,timed_out=false,sliceId=null,updated=0,created=0,deleted=26,batches=1,versionConflicts=0,noops=0,retries=2,throttledUntil=0s,bulk_failures=[],search_failures=[]]>

  at __randomizedtesting.SeedInfo.seed([B36AB6B5F42DB7E5:86367E10FB79DB4B]:0)
  at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
  at org.junit.Assert.assertThat(Assert.java:956)
  at org.junit.Assert.assertThat(Assert.java:923)
  at org.elasticsearch.reindex.DeleteByQueryBasicTests.testDeleteByQueryOnReadOnlyAllowDeleteIndex(DeleteByQueryBasicTests.java:265)
  at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java:-2)
  at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
  at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:568)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.invoke(RandomizedRunner.java:1758)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$8.evaluate(RandomizedRunner.java:946)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$9.evaluate(RandomizedRunner.java:982)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$10.evaluate(RandomizedRunner.java:996)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleSetupTeardownChained$1.evaluate(TestRuleSetupTeardownChained.java:48)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at org.apache.lucene.tests.util.TestRuleThreadAndTestName$1.evaluate(TestRuleThreadAndTestName.java:45)
  at org.apache.lucene.tests.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:60)
  at org.apache.lucene.tests.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:44)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:390)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl.forkTimeoutingTask(ThreadLeakControl.java:843)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$3.evaluate(ThreadLeakControl.java:490)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.runSingleTest(RandomizedRunner.java:955)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$5.evaluate(RandomizedRunner.java:840)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$6.evaluate(RandomizedRunner.java:891)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$7.evaluate(RandomizedRunner.java:902)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleStoreClassName$1.evaluate(TestRuleStoreClassName.java:38)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleAssertionsRequired$1.evaluate(TestRuleAssertionsRequired.java:53)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at org.apache.lucene.tests.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:44)
  at org.apache.lucene.tests.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:60)
  at org.apache.lucene.tests.util.TestRuleIgnoreTestSuites$1.evaluate(TestRuleIgnoreTestSuites.java:47)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:390)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl.lambda$forkTimeoutingTask$0(ThreadLeakControl.java:850)
  at java.lang.Thread.run(Thread.java:833)

```
modules/reindex/src/test/java/org/elasticsearch/reindex/DeleteByQueryBasicTests.java
for (Map.Entry<String, List<IndexRequestBuilder>> entry : docs.entrySet()) {
            assertHitCount(client().prepareSearch(entry.getKey()).setSize(0).get(), entry.getValue().size());
        }
        int slices = randomSlices(1, 10);
        int expectedSlices = expectedSliceStatuses(slices, docs.keySet());
        String[] sourceIndexNames = docs.keySet().toArray(new String[docs.size()]);
        assertThat(
            deleteByQuery().source(sourceIndexNames).filter(QueryBuilders.matchAllQuery()).refresh(true).setSlices(slices).get(),
            matcher().deleted(allDocs.size()).slices(hasSize(expectedSlices))
        );
        for (String index : docs.keySet()) {
            assertHitCount(client().prepareSearch(index).setSize(0).get(), 0);
        }
    }
    public void testMissingSources() {
        BulkByScrollResponse response = updateByQuery().source("missing-index-*")
            .refresh(true)
            .setSlices(AbstractBulkByScrollRequest.AUTO_SLICES)
            .get();
        assertThat(response, matcher().deleted(0).slices(hasSize(0)));
    }
    
    private void setDiskAllocationDeciderEnabled(boolean value) {
        Settings.Builder settings = value
            ? Settings.builder().putNull(DiskThresholdSettings.CLUSTER_ROUTING_ALLOCATION_DISK_THRESHOLD_ENABLED_SETTING.getKey())
            : Settings.builder().put(DiskThresholdSettings.CLUSTER_ROUTING_ALLOCATION_DISK_THRESHOLD_ENABLED_SETTING.getKey(), false);
        updateClusterSettings(settings);
    }
}