This didn't reproduce locally for me on my mac but my suspicion is it might be Windows related.

**Build scan:**
https://gradle-enterprise.elastic.co/s/eertquvftst2e/tests/:x-pack:plugin:security:test/org.elasticsearch.xpack.security.transport.netty4.SimpleSecurityNetty4ServerTransportTests/testClientChannelUsesSeparateSslConfigurationForRemoteCluster

**Reproduction line:**
```
gradlew ':x-pack:plugin:security:test' --tests "org.elasticsearch.xpack.security.transport.netty4.SimpleSecurityNetty4ServerTransportTests.testClientChannelUsesSeparateSslConfigurationForRemoteCluster" -Dtests.seed=AE878A5FDDFF0F54 -Dtests.locale=en-NZ -Dtests.timezone=US/Indiana-Starke -Druntime.java=20
```

**Applicable branches:**
main

**Reproduces locally?:**
No

**Failure history:**
https://gradle-enterprise.elastic.co/scans/tests?tests.container=org.elasticsearch.xpack.security.transport.netty4.SimpleSecurityNetty4ServerTransportTests&tests.test=testClientChannelUsesSeparateSslConfigurationForRemoteCluster

**Failure excerpt:**
```
java.lang.AssertionError: 
Expected: <100>
     but: was null

  at __randomizedtesting.SeedInfo.seed([AE878A5FDDFF0F54:1A613F99A3AFFDFF]: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.security.transport.netty4.SimpleSecurityNetty4ServerTransportTests.testClientChannelUsesSeparateSslConfigurationForRemoteCluster(SimpleSecurityNetty4ServerTransportTests.java:619)
  at jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
  at java.lang.reflect.Method.invoke(Method.java:578)
  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:1623)

```
x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/transport/netty4/SimpleSecurityNetty4ServerTransportTests.java
final Settings qcSettings2 = Settings.builder()
                .put("xpack.security.remote_cluster_client.ssl.verification_mode", "none")
                .put("remote_cluster.tcp.keep_alive", "false")
                .build();
            try (
                MockTransportService qcService = buildService("QC", Version.CURRENT, TransportVersion.CURRENT, qcSettings2);
                Transport.Connection connection = openConnection(qcService, node, connectionProfile)
            ) {
                assertThat(connection, instanceOf(StubbableTransport.WrappedConnection.class));
                Transport.Connection conn = ((StubbableTransport.WrappedConnection) connection).getConnection();
                assertThat(conn, instanceOf(TcpTransport.NodeChannels.class));
                TcpTransport.NodeChannels nodeChannels = (TcpTransport.NodeChannels) conn;
                for (TcpChannel channel : nodeChannels.getChannels()) {
                    assertFalse(channel.isServerChannel());
                    assertThat(channel.getProfile(), equalTo("_remote_cluster"));
                    final SSLEngine sslEngine = SSLEngineUtils.getSSLEngine(channel);
                    assertThat(sslEngine.getUseClientMode(), is(true));
                    assertThat(channel, instanceOf(Netty4TcpChannel.class));
                    final Map<String, Object> options = ((Netty4TcpChannel) channel).getNettyChannel()
                        .config()
                        .getOptions()
                        .entrySet()
                        .stream()
                        .filter(entry -> entry.getKey() instanceof NioChannelOption<?>)
                        .collect(Collectors.toUnmodifiableMap(entry -> entry.getKey().name(), Map.Entry::getValue));
                    assertThat(options.get(ChannelOption.SO_KEEPALIVE.name()), is(false));
                }
                final TcpChannel acceptedChannel = getAcceptedChannel(originalTransport, connection);
                assertThat(acceptedChannel.getProfile(), equalTo("_remote_cluster"));
            }