Four times in the last week there has been a hang in the System.Xaml in the CI tests. XamlBackgroundReader tests. Two on Linux/Intel64, two on Linux/Intel32. The most recent was today.
There is a set of tests that all call into a ReadTest() function, which does nothing but take in a path and reads it in the background. The failure is always one of these tests. The hang always occurs in XamlBackgroundReader.Read (), which WaitOnes on its ManualResetEvent and never gets woken up. See:
Koeplinger reviewed and believed this is an issue for the class library team.