This has been observed once in 9 b175 same binaries run;

----------messages:(5/354)----------
command: main -Dtest.insertDelay=true -Dtest.chunkSize=64 ManyRequests
reason: User specified action: run main/othervm/timeout=40 -Dtest.insertDelay=true -Dtest.chunkSize=64 ManyRequests
Mode: othervm [/othervm specified]
Additional options from @modules: --add-modules jdk.incubator.httpclient,java.logging,jdk.httpserver
elapsed time (seconds): 4.122
----------configuration:(3/80)----------
Boot Layer
  add modules: jdk.incubator.httpclient java.logging jdk.httpserver

----------System.out:(51/1937)----------
Sending 20 requests; delay=true, chunks=64, XFixed=false
Client: sendAsync: https://127.0.0.1:65439/foo/x1
Client: sendAsync: https://127.0.0.1:65439/foo/x2
Client: sendAsync: https://127.0.0.1:65439/foo/x3
Client: sendAsync: https://127.0.0.1:65439/foo/x4
Client: sendAsync: https://127.0.0.1:65439/foo/x5
Client: sendAsync: https://127.0.0.1:65439/foo/x6
Client: sendAsync: https://127.0.0.1:65439/foo/x7
Client: sendAsync: https://127.0.0.1:65439/foo/x8
Client: sendAsync: https://127.0.0.1:65439/foo/x9
Client: sendAsync: https://127.0.0.1:65439/foo/x10
Client: sendAsync: https://127.0.0.1:65439/foo/x11
Client: sendAsync: https://127.0.0.1:65439/foo/x12
Client: sendAsync: https://127.0.0.1:65439/foo/x13
Client: sendAsync: https://127.0.0.1:65439/foo/x14
Client: sendAsync: https://127.0.0.1:65439/foo/x15
Client: sendAsync: https://127.0.0.1:65439/foo/x16
Client: sendAsync: https://127.0.0.1:65439/foo/x17
Client: sendAsync: https://127.0.0.1:65439/foo/x18
Client: sendAsync: https://127.0.0.1:65439/foo/x19
Client: sendAsync: https://127.0.0.1:65439/foo/x20
Server: received /foo/x20
Result (1) from /foo/x20
Server: received /foo/x12
Result (2) from /foo/x12
Server: received /foo/x2
Result (3) from /foo/x2
Server: received /foo/x15
Result (4) from /foo/x15
Server: received /foo/x17
Result (5) from /foo/x17
Server: received /foo/x5
Result (6) from /foo/x5
Server: received /foo/x13
Result (7) from /foo/x13
Server: received /foo/x19
Result (8) from /foo/x19
Server: received /foo/x11
Result (9) from /foo/x11
Server: received /foo/x9
Result (10) from /foo/x9
Expected 200, got: 401 from /foo/x16
Expected 200, got: 401 from /foo/x1
Expected 200, got: 401 from /foo/x6
Expected 200, got: 401 from /foo/x18
Expected 200, got: 401 from /foo/x4
Expected 200, got: 401 from /foo/x3
Expected 200, got: 401 from /foo/x14
Expected 200, got: 401 from /foo/x7
Expected 200, got: 401 from /foo/x8
Expected 200, got: 401 from /foo/x10
----------System.err:(28/2145)----------
WARNING: Using incubator modules: jdk.incubator.httpclient
Jul 03, 2017 4:43:32 AM ManyRequests main
INFO: TEST
java.util.concurrent.CompletionException: java.io.IOException: Expected 200, got: 401
at java.base/java.util.concurrent.CompletableFuture.encodeRelay(CompletableFuture.java:367)
at java.base/java.util.concurrent.CompletableFuture.completeRelay(CompletableFuture.java:376)
at java.base/java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:1074)
at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:506)
at java.base/java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:2073)
at jdk.incubator.httpclient/jdk.incubator.http.ResponseProcessors$ByteArrayProcessor.onComplete(ResponseProcessors.java:219)
at jdk.incubator.httpclient/jdk.incubator.http.BlockingPushPublisher.acceptData(BlockingPushPublisher.java:65)
at jdk.incubator.httpclient/jdk.incubator.http.AbstractPushPublisher.consume(AbstractPushPublisher.java:51)
at jdk.incubator.httpclient/jdk.incubator.http.ResponseContent.pushBodyChunked(ResponseContent.java:234)
at jdk.incubator.httpclient/jdk.incubator.http.ResponseContent.pushBody(ResponseContent.java:110)
at jdk.incubator.httpclient/jdk.incubator.http.Http1Response.lambda$readBody$2(Http1Response.java:161)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1161)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
at java.base/java.lang.Thread.run(Thread.java:844)
Caused by: java.io.IOException: Expected 200, got: 401
at ManyRequests.completedWithIOException(ManyRequests.java:183)
at ManyRequests.lambda$test$2(ManyRequests.java:159)
at java.base/java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:1072)
... 11 more