GetAsync_ContentCanBeCanceled test is failing in CI

[wfurt]

The test fails with System.IO.IOException:

   at System.Net.Test.Common.LoopbackServer.Connection.ReadRequestHeaderBytesAsync() in /_/src/libraries/Common/tests/System/Net/Http/LoopbackServer.cs:line 670
   at System.Net.Test.Common.LoopbackServer.Connection.ReadRequestDataAsync(Boolean readBody) in /_/src/libraries/Common/tests/System/Net/Http/LoopbackServer.cs:line 716
   at System.Net.Http.Functional.Tests.HttpClientTest.<>c__DisplayClass26_0.<<GetAsync_ContentCanBeCanceled>b__3>d.MoveNext() in /_/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientTest.cs:line 481
--- End of stack trace from previous location ---
   at System.Net.Test.Common.LoopbackServer.AcceptConnectionAsync(Func`2 funcAsync) in /_/src/libraries/Common/tests/System/Net/Http/LoopbackServer.cs:line 124
   at System.Net.Http.Functional.Tests.HttpClientTest.<>c__DisplayClass26_0.<<GetAsync_ContentCanBeCanceled>b__1>d.MoveNext() in /_/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientTest.cs:line 479
--- End of stack trace from previous location ---
   at System.Threading.Tasks.TaskTimeoutExtensions.WhenAllOrAnyFailed(Task[] tasks) in /_/src/libraries/Common/tests/System/Threading/Tasks/TaskTimeoutExtensions.cs:line 96
   at System.Threading.Tasks.TaskTimeoutExtensions.WhenAllOrAnyFailed(Task[] tasks) in /_/src/libraries/Common/tests/System/Threading/Tasks/TaskTimeoutExtensions.cs:line 124
   at System.Net.Test.Common.LoopbackServerFactory.<>c__DisplayClass5_0.<<CreateClientAndServerAsync>b__0>d.MoveNext() in /_/src/libraries/Common/tests/System/Net/Http/GenericLoopbackServer.cs:line 36
--- End of stack trace from previous location ---
   at System.Net.Test.Common.LoopbackServer.CreateServerAsync(Func`2 funcAsync, Options options) in /_/src/libraries/Common/tests/System/Net/Http/LoopbackServer.cs:line 72
   at System.Threading.Tasks.TaskTimeoutExtensions.TimeoutAfter(Task task, TimeSpan timeout) in /_/src/libraries/Common/tests/System/Threading/Tasks/TaskTimeoutExtensions.cs:line 37
   at System.Net.Http.Functional.Tests.HttpClientTest.GetAsync_ContentCanBeCanceled(Int32 getMode, Int32 cancelMode) in /_/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientTest.cs:line 444
--- End of stack trace from previous location ---

I did query for last 90 days and first occurrence is 10/1 and 227 failures after that.
That seems to strongly correlate with #42346. cc: @stephentoub

So far I was unable to reproduce it locally.
In attempt to reproduce I've seen similar traces when Loopback server fails to retrieve particular part of HTTP while cancelling. (like PostAsyncNonDuplex_ServerCompletesResponseBodyThenResetsStreamWithNoError_SuccessAndRequestBodyCancelled.

So I'm wondering if this is 1) problem with Loopback server unable to handle partial request, 2) test bug as the cancelling tests should ignore server side failures or 3) product bug when we perhaps don't handle something right. (the second test fails to read H/2 Frame)

cc: @geoffkizer

[ghost]

Tagging subscribers to this area: @dotnet/ncl
See info in area-owners.md if you want to be subscribed.