Using Debian 9. YMMV. This is intended to be be a single administrator backup solution for my home and as such, using the Linux duplicati server on port 8200 not 8300 (service mode). Took me awhile to figure out the difference and which would be more appropriate. I also installed on my other two windows machines since they’re intended to be the clients and I need the practice. I administer through the web browser on the Linux server itself using localhost:8200.
Are you attempting to access locally or remotely? If locally, did your upgrade any change file permissions? I created a “duplicati” user and added my personal login and duplicati to an already existing group “backup”. Changed target backup directories and other relevant non system duplicati directories to owner=backup rwx, group=backup, world=r-x. This is mainly for security. Everyone else will need to sudo to mess things up, but it could also mess up an upgrade. I also went through the permissions thing setting up Dupllication Windows 10 (much more difficult!) and ran into permission problems mostly of my own making.
Have you done anything else unrelated that could mess up iptables or your AV on any of the servers or client machines?
The only time I need to login (besides admin setup) is first use of the GUI or extended idle time No worries after that.
You didn’t say, but are any of your clients Windows? I’m also going to be setting something like this up for my church full of non-techies and want this to be as simple as possible to understand and use, that’s why I’m going Duplicati. It’s all windows boxes and Duplicati is simple all the way around, but setting up an IIIS vanilla FTP server NOT. You will have to dork with permissions in Windows to just get it to sign on., much less transfer files. Still haven’t gotten it right