Summary of latest 60(to 28/6/2026) CI failures.

### Version

5.x 5.x-stable

### Context

I had trouble getting a green CI build of my https proxy PR #6215. In my effort to determine whether the failures I was seeing were due to my changes I did an analysis of the past failures to see if these failure preexisted due to flaky tests.

I decided to publish the report in case it is useful and to serve as a meta ticket to tackle these flaky test failures. I also added a column to link related PRs or issues. I have posted a PR with a suggested fix for `NetTest.testListenDomainSocketAddress[Native]` #6217

| Frequency | Test | Error | Related issues / PRs |
|---|---|---|---|
| 9/60 (15%) | `NetTest.testEndHandlerCalledAfterAllEmissions` | IllegalState "Timed out" | #6219 |
| 7/60 (11.7%) | Http2 `*HeadersPutAll` / `testResponseTrailers*` | Illegal 'TE' header value / Stream reset | |
| 4/60 (6.7%) | `Http2*.testSslHandshakeTimeout` | Timeout Unsatisfied checkpoint | |
| 4/60 (6.7%) | `NetTest.testListenDomainSocketAddress[Native]` | leftover `.sock` / native timeout | #6217 |
| 3/60 (5%) | `it.networklogging.NetTest.testServerLogging` / `testNoLogging` | Timeout (120 s) | |
| 2/60 (3.3%) | `WebSocketTest.*` (4 methods across 2 runs) | Timeout Unsatisfied checkpoint | |
| 2/60 (3.3%) | `Http1xProxyTest.testNonProxyHosts3` | Bind "Address already in use" | |
| 2/60 (3.3%) | `Http1xSendFileTest.testSendOpenRangeFileFromClasspath` | | |
| 2/60 (3.3%) | `MetricsTest.testThreadPoolMetrics*` (windows) | | |
| 2/60 (3.3%) | `NetTest.testServerWithIdleTimeoutSendChunkedFile` | | |
| 1/60 (1.7%) | `NetBandwidthLimitingTest.fileUploadIsThrottled` | Timeout (120 s) | |
| 1/60 (1.7%) | `DNSTest.*` (windows) | Bind "Address already in use" | |
| 1/60 (1.7%) | `SynchronizationTest.*` (4.x, windows) | | |
| 1/60 (1.7%) | `NetTest.testCloseUnwritableSocket` | | |
| 1/60 (1.7%) | `HttpsProxyTest.testHttpsProxy_Http2Origin_tunnelled` | | |
| 1/60 (1.7%) | `SharedHttpClientTest.testSharedPoolRetainedByOtherDeployment` | | |
| 1/60 (1.7%) | `Http3Test>HttpTest.testResponseTrailers` | | |
| 1/60 (1.7%) | `Http2MetricsTest…testHttpClientMetricsQueueClose` | | |
| 1/60 (1.7%) | `Http1xTest.testInvalidChunkInHttpServerRequest` | Timeout Unsatisfied checkpoint | |
| 1/60 (1.7%) | `SSLEngineTest.testWebSocketDefaultEngine` | Timeout Unsatisfied checkpoint | |

Use the failure table as the entry point and inspect the named tests, especially NetTest.testEndHandlerCalledAfterAllEmissions and the Http2, WebSocket, proxy, and DNS failures. Review related PRs #6217 and #6219, then reproduce the failures in CI to determine which are flaky and which are regressions. Done means the reported failures have documented causes and targeted fixes or follow-up issues.

Written by the indexing model from the issue text.