Restore, Upgrade: Connection to server is lost

I am reinstalling Duplicati after a disk crash. I was running Linux MInt 18.3 and Duplicati 2-something, not the latest. Now I am at Linux Mint 19.3 and Duplicati, latest. I used Aptik to restore my environment so some old versions of my config files were restored. They could be pre-v2; don’t know.
Upon opening Duplicati I see my configurations and the status says
Verifying backend data
Then “Connection to server is lost, attempting again” loops until the program quits.

That sounds like Duplicati went down, but that should result in a browser loop saying:

Connection lost
The connection to the server is lost, attempting again in 0:02 …

What’s the sign of the program quitting? Any info from ps command or systemctl status duplicati?

It also mentions one of your jobs, right? Does that run on a schedule? I’d guess it thinks it should run now. Keeping it from doing that might be key to getting a look at things. Can you quickly edit that job and turn off schedule for current day of the week and save that? You want Duplicati to start and stay up while you look for error information in places like About --> Show log or <job> --> Show log. If none, may need to add log.

That wasn’t status bar but a red popup at bottom of screen, right? Any info in the box? If not try logs above.

Because I’m guessing you restored some old ~/.config/Duplicati files (whose dates might already updated due to the activity you mentioned), try not to run Repair because it can look at a stale database and current destination and decide the destination has extra files – and delete them, which is not likely the fix you want.

One thing to check is what mono --version says. It should be at least 5, otherwise install mono-complete.

Upgrading mono from 4* to 6* seems to have fixed it. Thanks.