runtime: UnixDomainSocket test is timing out

The recently added test ConcurrentSendReceive has failed in official runs with the following error 1-2 times a day for the last three days:

System.TimeoutException : WhenAllOrAnyFailed timed out after 10000
   at System.Threading.Tasks.TaskTimeoutExtensions.WhenAllOrAnyFailed(Task[] tasks, Int32 millisecondsTimeout)
   at System.Net.Sockets.Tests.UnixDomainSocketTest.ConcurrentSendReceive(Boolean forceNonBlocking) in E:\A\_work\2\s\corefx\src\System.Net.Sockets\tests\FunctionalTests\UnixDomainSocketTest.netcoreapp.cs:line 284
--- End of stack trace from previous location where exception was thrown ---

The failures occur for both the blocking and non-blocking case, and has occurred exclusively on the Windows.10.Amd64.ClientRS4 leg.

I’m not sure if that means Unix domain sockets are not enabled in RS4, if there is some config that needs to happen on that machine, or if there is a real bug here.