[ci-scan] Recurring: CreateTimerNonRepeatingDoesNotRepeat fails with NullReferenceException on macOS ARM64 (maui-pr)

Summary

DispatcherTests.CreateTimerNonRepeatingDoesNotRepeat fails with a NullReferenceException inside the timer callback's async state machine on osx.15.arm64.maui.open, breaking the latest main build.

Build Information

• Pipeline: maui-pr (definition 302)
• Build: 1459938
• Branch: main
• First seen: 2026-06-11
• Occurrences: 1 in the last 10 builds (current build is red)

Affected Legs

• macOS 15 ARM64 — Windows Helix Unit Tests (Debug) → Helix queue osx.15.arm64.maui.open
• Work item: Microsoft.Maui.UnitTests.dll (ExitCode 1)

Error Message

CreateTimerNonRepeatingDoesNotRepeat [FAIL]
  System.NullReferenceException : Object reference not set to an instance of an object.
  Stack Trace:
    /_/src/Core/tests/UnitTests/Dispatching/DispatcherTests.cs(140,0):
      at Microsoft.Maui.UnitTests.Dispatching.DispatcherTests.<>c
           .<<CreateTimerNonRepeatingDoesNotRepeat>b__10_0>d.MoveNext()
    /_/src/Core/tests/UnitTests/TestClasses/DispatcherStub.cs(148,0):
      at Microsoft.Maui.UnitTests.DispatcherTest.<>c__DisplayClass1_0
           .<<Run>b__0>d.MoveNext()

Microsoft.Maui.UnitTests  Total: 834, Errors: 0, Failed: 1, Skipped: 3

Recommended Action

Investigate DispatcherTests.cs line 140 and DispatcherStub.cs line 148 in src/Core/tests/UnitTests/. The test verifies a non-repeating timer fires exactly once and stops. The NullReferenceException in the async callback suggests the dispatcher's internal timer state or task completion source is null when the callback fires — possibly a race condition or an object that was already disposed. Check recent changes to DispatcherStub (the test helper) or the IDispatcher timer implementation under src/Core/src/Dispatching/.

Generated by CI Failure Scanner · sonnet46 6M · ◷

Start with src/Core/tests/UnitTests/Dispatching/DispatcherTests.cs at line 140 and src/Core/tests/UnitTests/TestClasses/DispatcherStub.cs at line 148, then inspect the timer implementation under src/Core/src/Dispatching/. Reproduce the failure on the osx.15.arm64.maui.open leg and check recent DispatcherStub changes. Done means CreateTimerNonRepeatingDoesNotRepeat fires exactly once without a NullReferenceException and the unit test passes.