Thanks for the information - and don’t worry about taking time to respond - we all have the real world to deal with. 
The Log lines you provided confirm that the backup got to the final testing step where it checks one each of dblock, dlist, and dindex files after each backup to make sure they’re still valid.
I’m not sure which guidelines you mean, do you have a link to the configuration guidelines you think should be updated?
I tested again using a physical cable pull as you suggested but still am not seeing the issue you reported. (Though I did pull the cable before I started the job, not while it was running.)
My test job was to a local folder and finished without problem, though it did display a “1 warning” message. By going to main menu “About” → “Show log” → “Live” and selecting “Warning” I saw the (expected) error below.
In your first screenshot it looks like Duplicati is stuck “Waiting for upload”. Are you sure your backup job was to a local (to the computer) destination?
I ask because there is a known issue where if the network connection is interrupted DURING an upload, then Duplicati can get stuck waiting for the interrupted upload to finish. But I’ve only see that be an issue during uploads, not during emails.
Jun 22, 2018 10:50 AM: Failed to send message: MailKit.Net.Smtp.SmtpCommandException: Cannot connect to SMTP server ###.###.###.### (###.###.###.###:##), connect error 10065
{"ClassName":"MailKit.Net.Smtp.SmtpCommandException",
"Message":"Cannot connect to SMTP server ###.###.###.### (###.###.###.###:##), connect error 10065",
"Data":null,
"InnerException":null,
"HelpURL":"https://github.com/jstedfast/MailKit/blob/master/FAQ.md#ProtocolLog",
"StackTraceString":" at Duplicati.Library.Modules.Builtin.SendMail.SendMessage(String subject, String body)
at Duplicati.Library.Modules.Builtin.ReportHelper.OnFinish(Object result)",
"RemoteStackTraceString":null,
"RemoteStackIndex":0,
"ExceptionMethod":"8
SendMessage
Duplicati.Library.Modules.Builtin, Version=2.0.3.7, Culture=neutral, PublicKeyToken=null
Duplicati.Library.Modules.Builtin.SendMail
Void SendMessage(System.String, System.String)",
"HResult":-2146233088,
"Source":"Duplicati.Library.Modules.Builtin",
"WatsonBuckets":null,
"Mailbox":"",
"ErrorCode":"UnexpectedStatusCode",
"StatusCode":"ServiceNotAvailable"}