This is responsible for vast majority of the failures of windows_opt job.
https://fusion.corp.google.com/projectanalysis/current/KOKORO/prod%3Agrpc%2Fcore%2Fmaster%2Fwindows%2Fgrpc_basictests_opt

The flakiness rate is pretty high (> 20%)

A rew recent occurrences:
https://source.cloud.google.com/results/invocations/3f22e6c6-c5d9-4420-b414-9a7bd9cfc1d6/targets/github%2Fgrpc%2Fpython_windows_opt_gevent/tests
https://source.cloud.google.com/results/invocations/f694442c-e08f-493c-9fb3-d1bc48abe174/targets/github%2Fgrpc%2Fpython_windows_opt_gevent/tests
https://source.cloud.google.com/results/invocations/4f1686e1-68a3-48c9-b65b-b45f0f5f82d7/targets/github%2Fgrpc%2Fpython_windows_opt_gevent/tests