[net11][CoreCLR] Essentials FileSystem_Tests NullReferenceException in FileStream.ReadAsync on iOS/MacCatalyst device tests

Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1497568 Leg Name: maui-pr-devicetests / net11.0 CoreCLR iOS Helix Tests (Run DeviceTests iOS) and net11.0 CoreCLR MacCatalyst Helix Tests (Run DeviceTests MacCatalyst)

Error Details

Microsoft.Maui.Essentials.DeviceTests.FileSystem_Tests fail on the net11 CoreCLR iOS and MacCatalyst device-test legs with a NullReferenceException thrown from System.IO.FileStream.ReadAsync. Affected tests include CheckFileResultOpenReadAsyncMultipleTimes and every OpenAppPackageFileAsync_Can_Load_File case (5 failures per leg). The non-zero XHarness exit also surfaces as a work-item level WorkItemExecution failure for the same Essentials work item.

System.NullReferenceException : Arg_NullReferenceException
   at System.IO.FileStream.ReadAsync(Memory`1 buffer, CancellationToken cancellationToken)
   at System.IO.StreamReader.ReadBufferAsync(CancellationToken cancellationToken)
   at System.IO.StreamReader.ReadToEndAsyncInternal(CancellationToken cancellationToken)
   at Microsoft.Maui.Essentials.DeviceTests.FileSystem_Tests.CheckFileResultOpenReadAsyncMultipleTimes()
--- End of stack trace from previous location ---

Error Message

{
    "ErrorMessage": [
        "at System.IO.FileStream.ReadAsync",
        "at Microsoft.Maui.Essentials.DeviceTests.FileSystem_Tests."
    ],
    "BuildRetry": false,
    "ExcludeConsoleLog": false
}

Known issue validation

Build: :mag_right: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1497568 Error message validated: [at System.IO.FileStream.ReadAsync at Microsoft.Maui.Essentials.DeviceTests.FileSystem_Tests.] Result validation: :white_check_mark: Known issue matched with the provided build. Validation performed at: 7/7/2026 8:47:43 PM UTC

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Summary