While working on dotnet/macios#6196 the following BCL tests failed on iOS simulator and device:

• All tests in class System.Net.Security.Tests.SslStreamSniTest
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_IndividualServerVsAllClientSupportedProtocols_Success(serverProtocol: Tls)
• System.Net.Security.Tests.ClientDefaultEncryptionTest.ClientDefaultEncryption_ServerRequireEncryption_ConnectWithEncryption
• System.Net.Security.Tests.ClientDefaultEncryptionTest.ClientDefaultEncryption_ServerAllowNoEncryption_ConnectWithEncryption
• System.Net.Security.Tests.ServerRequireEncryptionTest.ServerRequireEncryption_ClientRequireEncryption_ConnectWithEncryption
• System.Net.Security.Tests.ServerAllowNoEncryptionTest.ServerAllowNoEncryption_ClientAllowNoEncryption_ConnectWithEncryption
• System.Net.Security.Tests.CertificateValidationRemoteServer.CertificateValidationRemoteServer_EndToEnd_Ok
• System.Net.Security.Tests.ServerAllowNoEncryptionTest.ServerAllowNoEncryption_ClientRequireEncryption_ConnectWithEncryption
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_EachSupportedProtocol_Success(protocol: Default)
• System.Net.Security.Tests.ServerRequireEncryptionTest.ServerRequireEncryption_ClientAllowNoEncryption_ConnectWithEncryption
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_EachSupportedProtocol_Success(protocol: Ssl3)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_MismatchProtocols_Fails(serverProtocol: Tls12, clientProtocol: Tls, expectedException: typeof(System.Security.Authentication.AuthenticationException))
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_MismatchProtocols_Fails(serverProtocol: Tls11, clientProtocol: Tls12, expectedException: typeof(System.IO.IOException))
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_AllServerAllClient_Success
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_MismatchProtocols_Fails(serverProtocol: Tls, clientProtocol: Tls12, expectedException: typeof(System.IO.IOException))
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_IndividualServerVsAllClientSupportedProtocols_Success(serverProtocol: Tls11)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_MismatchProtocols_Fails(serverProtocol: Tls11, clientProtocol: Tls, expectedException: typeof(System.Security.Authentication.AuthenticationException))
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_EachSupportedProtocol_Success(protocol: Tls)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_EachSupportedProtocol_Success(protocol: Tls12)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_ServerRequireEncryption_ConnectWithEncryption
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_AllServerVsIndividualClientSupportedProtocols_Success(clientProtocol: Tls)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_AllServerVsIndividualClientSupportedProtocols_Success(clientProtocol: Ssl3)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_AllServerVsIndividualClientSupportedProtocols_Success(clientProtocol: Default)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_MismatchProtocols_Fails(serverProtocol: Tls12, clientProtocol: Tls11, expectedException: typeof(System.Security.Authentication.AuthenticationException))
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_MismatchProtocols_Fails(serverProtocol: Tls, clientProtocol: Tls11, expectedException: typeof(System.IO.IOException))
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_IndividualServerVsAllClientSupportedProtocols_Success(serverProtocol: Ssl3)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_IndividualServerVsAllClientSupportedProtocols_Success(serverProtocol: Tls12)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_EachSupportedProtocol_Success(protocol: Tls11)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_IndividualServerVsAllClientSupportedProtocols_Success(serverProtocol: Default)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_AllServerVsIndividualClientSupportedProtocols_Success(clientProtocol: Tls12)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_AllServerVsIndividualClientSupportedProtocols_Success(clientProtocol: Tls11)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_AllServerVsIndividualClientSupportedProtocols_Success(clientProtocol: Tls11)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_AllServerVsIndividualClientSupportedProtocols_Success(clientProtocol: Tls11)
• System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_SslStreamClientServerNone_UseStrongCryptoSet

During the execution of the tests, the following crash was shown in the logs (which looks to be related to the network stack code).

Tests have been ignored in the xamarin-macios 2019-06 branch, but should be re-enabled.