For example:
https://evergreen.mongodb.com/task/dot_net_driver_secure_tests_linux__version~5.0_os~ubuntu_1804_topology~replicaset_auth~auth_ssl~ssl_test_netstandard21_patch_b961b81cb7dc1ffe7262c55a227afad0aab5a994_6138ff3a9ccd4e2b269ec32e_21_09_08_18_22_08
https://evergreen.mongodb.com/task/dot_net_driver_secure_tests_macOS__version~5.0_os~macos_1014_topology~standalone_auth~auth_ssl~ssl_test_netstandard21_patch_b961b81cb7dc1ffe7262c55a227afad0aab5a994_6139469732f4171b6671f7b2_21_09_08_23_26_33

Leads to timeouts due to hanging DisposableMongoClient.Dispose(). Was not able to reproduce locally.
From brief investigation two flavors where observed:

• Execution blocked at monitorCancellationTokenSource.Cancel(); in ServerMonitor.Dispose()
• Execution blocked at _cancellationTokenSource.Cancel(); in RoundTripTimeMonitor.Dispose()