Keep Alive triggering errors

[c9mb]

Issue description

It's a bit inconsistent, but I am getting errors logged of the form:

Message:
Failed (at "https://www.mydomainname.com.:443/umbraco").
									
Exception:
System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Net.WebException: The request was aborted: Could not create SSL/TLS secure channel.
   at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
   at System.Net.Http.HttpClientHandler.GetResponseCallback(IAsyncResult ar)
   --- End of inner exception stack trace ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Umbraco.Web.Scheduling.KeepAlive.<PerformRunAsync>d__5.MoveNext()

I guess that the dot at the end of the domain - before the :443 - being the possible candidate.

When this happens it logs this error at 5min intervals.