I've seen this test failing on Windows 10 amd64/x86 on a PR with changes that were unrelated (only touching PAL tests).

The error is
Assert.Throws() Failure
Expected: typeof(System.IO.FileNotFoundException)
Actual: (No exception was thrown)

https://dev.azure.com/dnceng/public/_build/results?buildId=1157809&view=ms.vss-test-web.build-test-results-tab&runId=34956638&resultId=113343

The history of the failure shows that it has been failing this way intermittently since May 19 which actually looks like a day when the test was added.