First, make sure you’re on the service. Besides port 8200, you can also look over About → System info.
UserName is probably the easiest way to recognize a Windows service. Do you even also run TrayIcon?
Finding the reason would be good. Autoupdates that become corrupted are ignored, leaving you with the .msi install in C:\Program Files\Duplicati 2 which is an old version until you install new from .msi.
is where to look, but detecting corruptions may be a bit hard. Easy test is to sort by date. Any too new?
You coule rename the folder, autoupdate again, then compare them, e.g. do all folder statistics match?
EDIT:
Backup failed - Error in updater was a similar problem. There the corruption was caused by extra data.
I’m not sure where the message would appear. Maybe look in About → Show log → Stored for startup?