It should be 18 if you are only accessing RuntimePermission.GetSafeDirDefaultExternal.
What is the output of Log(LastException) in Client_Connected?
Make a test, put the device in airplane mode and enable wifi (cellular network should be disabled). Does it work? Android will prefer the network with internet connection.
thank you,
I do not currently have the Android 9 smart phone to control the Log(LastException) in Client_Connected.
I will do the tests as soon as I get the SP.