The test has been observed failing in timeout. The SelectorManager thread seems to be blocked trying to acquire a lock on PrintStream (System.err).

"HttpClient-18-SelectorManager" #614 [4144544] daemon prio=5 os_prio=0 cpu=19.93ms elapsed=484.07s allocated=514K defined_classes=0 tid=0x0000ffff48347410 nid=4144544 waiting on condition [0x0000fffeda00d000]
   java.lang.Thread.State: WAITING (parking)
at jdk.internal.misc.Unsafe.park(java.base@22-internal/Native Method)
- parking to wait for <0x00000000d023fe08> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
at java.util.concurrent.locks.LockSupport.park(java.base@22-internal/LockSupport.java:221)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(java.base@22-internal/AbstractQueuedSynchronizer.java:754)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(java.base@22-internal/AbstractQueuedSynchronizer.java:990)
at java.util.concurrent.locks.ReentrantLock$Sync.lock(java.base@22-internal/ReentrantLock.java:153)
at java.util.concurrent.locks.ReentrantLock.lock(java.base@22-internal/ReentrantLock.java:322)
at jdk.internal.misc.InternalLock.lock(java.base@22-internal/InternalLock.java:74)
at java.io.PrintStream.writeln(java.base@22-internal/PrintStream.java:824)
at java.io.PrintStream.println(java.base@22-internal/PrintStream.java:1168)
at jdk.internal.net.http.common.DebugLogger.print(java.net.http@22-internal/DebugLogger.java:293)
at jdk.internal.net.http.common.DebugLogger.log(java.net.http@22-internal/DebugLogger.java:241)
at java.lang.System$Logger.log(java.base@22-internal/System.java:1387)
at jdk.internal.net.http.common.Logger.log(java.net.http@22-internal/Logger.java:72)
at jdk.internal.net.http.SocketTube$InternalReadPublisher$ReadSubscription.signalCompletion(java.net.http@22-internal/SocketTube.java:644)
at jdk.internal.net.http.SocketTube$InternalReadPublisher$InternalReadSubscription.read(java.net.http@22-internal/SocketTube.java:829)
at jdk.internal.net.http.SocketTube$InternalReadPublisher$InternalReadSubscription$$Lambda/0x0000020001173d00.run(java.net.http@22-internal/Unknown Source)
at jdk.internal.net.http.SocketTube$SocketFlowTask.run(java.net.http@22-internal/SocketTube.java:181)
at jdk.internal.net.http.common.SequentialScheduler$SchedulableTask.run(java.net.http@22-internal/SequentialScheduler.java:207)
at jdk.internal.net.http.common.SequentialScheduler.runOrSchedule(java.net.http@22-internal/SequentialScheduler.java:280)
at jdk.internal.net.http.common.SequentialScheduler.runOrSchedule(java.net.http@22-internal/SequentialScheduler.java:233)
at jdk.internal.net.http.SocketTube$InternalReadPublisher$InternalReadSubscription.signalError(java.net.http@22-internal/SocketTube.java:778)
at jdk.internal.net.http.SocketTube.signalClosed(java.net.http@22-internal/SocketTube.java:159)
at jdk.internal.net.http.PlainHttpConnection.close(java.net.http@22-internal/PlainHttpConnection.java:428)
at jdk.internal.net.http.PlainHttpConnection.close(java.net.http@22-internal/PlainHttpConnection.java:406)
at jdk.internal.net.http.AsyncSSLConnection.close(java.net.http@22-internal/AsyncSSLConnection.java:111)
at jdk.internal.net.http.Http2Connection.shutdown(java.net.http@22-internal/Http2Connection.java:824)
at jdk.internal.net.http.Http2Connection$IdleConnectionTimeoutEvent.handle(java.net.http@22-internal/Http2Connection.java:240)
at jdk.internal.net.http.HttpClientImpl.purgeTimeoutsAndReturnNextDeadline(java.net.http@22-internal/HttpClientImpl.java:1782)
at jdk.internal.net.http.HttpClientImpl$SelectorManager.run(java.net.http@22-internal/HttpClientImpl.java:1379)