When i did an initial 65gb backup from an external USB 2.0 drive to a local Ubuntu box via SFTP, the progress bar showed very low transfer rates around 15 KB/s. When I came back after an hour the transfer had frozen so I tried pausing and resuming, but Duplicati had nothing to resume. The backup was listed as never run.
However, after restarting the browser, the backup was listed as completed in just about an hour, and it works fine - I can add and restore files from it. So the UX had frozen somehow.
This never happens when I do backups from internal SSD:s, so I’m guessing it has to do with the USB drive?
Is it possible the machine went to sleep while you were away? I’ve been seeing an increase in reports of “stalls” happening when the backup destination disappears…
The server is an Ubuntu box that should be constantly running, but it is possible that the client machine (Windows 10) did something. Maybe USB power save interfered with the transfer - USB peripherals can get interrupted when the machine is left unattended for a while even when USB tasks are running, and without any hibernation or sleep. Again, backing up from SSD:s have never been a problem so this is my best theory at the moment 
Unlike myself, USB devices generally don’t fall asleep while they’re in use. 
But if Duplicati spent enough time gathering blocks to build a file to be sent to the drive then it (the drive) might have taken a short nap…
Of course as you mentioned this is all just theory for now (though the stalling issue with disconnected destinations is a known problem).
If it’s just a user experience issue and not causing actual errors in the backup I’d suggest we wait until the disconnected destination issue is resolved and see if this goes away with it.
However, if you’re finding your backups are actually incomplete or failing then we can try digging a bit more.
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