That is a “first install” issue that has not been fixed yet. Once you get a real error (i.e. force stop a running backup to trigger it), you will get a popup with the error, and clicking “Dismiss” will make it work like normal again.
Glacier is a bit problematic, due to the restore process and it has not been fully automated (nor integrated in Duplicati). It works by using the S3 life-cycle rules to move files to Glacier. This means that Duplicati can no longer verify that all is working as expected, so you need to “trust” it, which is a bad idea.
To test the restore, you basically have to recall the files from Glacier. If you can get them moved back into S3, you can test the restore.
I generally recommend not using Glacier with Duplicati for these reasons.
Duplicati 1.3.x did not like this, but with Duplicati 2.0 there is no dependence on path, so you can move/add/remove/rename root folders as much as you like. The only downside is that if the path changes, Duplicati needs to re-scan the file, as opposed to just checking the filestamp which can take longer.
That option makes Duplicati listen to network requests from outside the machine. It requires that you restart Duplicati for it to take effect.
If you have systemd, it should be as simple as:
systemctl duplicati start
This will run a server in the background, you can get the tray-icon up and connected with this command:
duplicati --no-hosted-server --hosturl=http://localhost:8200
I think this will solve your problem: SSL TLS support in Mono · duplicati/duplicati Wiki · GitHub