**Build scan:**
https://gradle-enterprise.elastic.co/s/qcgnnfs5y74ug/tests/:x-pack:plugin:autoscaling:test/org.elasticsearch.xpack.autoscaling.storage.ReactiveStorageDeciderServiceTests/testNodeSizeForDataBelowLowWatermark

**Reproduction line:**
`gradlew ':x-pack:plugin:autoscaling:test' --tests "org.elasticsearch.xpack.autoscaling.storage.ReactiveStorageDeciderServiceTests.testNodeSizeForDataBelowLowWatermark" -Dtests.seed=39CAF34D3996EB47 -Dtests.locale=es-ES -Dtests.timezone=US/Hawaii -Druntime.java=18`

**Applicable branches:**
master

**Reproduces locally?:**
Didn't try

**Failure history:**
https://gradle-enterprise.elastic.co/scans/tests?tests.container=org.elasticsearch.xpack.autoscaling.storage.ReactiveStorageDeciderServiceTests&tests.test=testNodeSizeForDataBelowLowWatermark

**Failure excerpt:**
```
java.lang.AssertionError: 
Expected: <21800L>
     but: was <21799L>

  at __randomizedtesting.SeedInfo.seed([39CAF34D3996EB47:4A70D135F051CD25]: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.xpack.autoscaling.storage.ReactiveStorageDeciderServiceTests.testNodeSizeForDataBelowLowWatermark(ReactiveStorageDeciderServiceTests.java:372)
  at jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
  at java.lang.reflect.Method.invoke(Method.java:577)
  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:44)
  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)

```
x-pack/plugin/autoscaling/src/main/java/org/elasticsearch/xpack/autoscaling/storage/ReactiveStorageDeciderService.java
for (ShardRouting shard : routingNode) {
                    if (shard.started()
                        && canRemainOnlyHighestTierPreference(shard, allocation) == false
                        && canAllocate(shard, allocation) == false) {
                        candidates.add(shard);
                    }
                }
            }
            
            Set<ShardRouting> unmovableShards = candidates.stream()
                .filter(s -> allocatedToTier(s, allocation))
                .filter(s -> cannotRemainDueToStorage(s, allocation))
                .collect(Collectors.toSet());
            long unmovableBytes = unmovableShards.stream()
                .collect(Collectors.groupingBy(ShardRouting::currentNodeId))
                .entrySet()
                .stream()
                .mapToLong(e -> unmovableSize(e.getKey(), e.getValue()))
                .sum();
            List<ShardRouting> unallocatedShards = candidates.stream()
                .filter(Predicate.not(unmovableShards::contains))
                .filter(s1 -> cannotAllocateDueToStorage(s1, allocation))
                .toList();
            long unallocatableBytes = unallocatedShards.stream().mapToLong(this::sizeOf).sum();
            return new ShardsSize(
                unallocatableBytes + unmovableBytes,
                Stream.concat(unmovableShards.stream(), unallocatedShards.stream())
                    .map(ShardRouting::shardId)
                    .collect(Collectors.toCollection(TreeSet::new))
            );