Error while running backup, but where are the logs?

I’m testing Duplicati (latest version) on macOS (High Sierra). The remote backup place is a SFTP server.

Duplicati ran all night to backup most of my Mac. However I found a message “Error while running Backup, one or more errors occurred”. Clicked on “Show” but the log does not seem to include any error messages. How are they supposed to appear? Also got the message: “Last successful run: never.”
Checked on the SFTP server and found many “.aes” files, which are expected I suppose.

Now I’m worried. Did my backup go fine? Can I trust Duplicati? Where are the actual error log files and how can I be sure that the backup is valid?

Thanks for any help!

Backup was set to run every night. The next night I got (finally!) an actual error message in a red dialog box: “Error while running Backup / Unexpected difference in fileset version 1: 12/18/2018 9:44:52 PM (database id: 1), found 667591 entries, but expected 671921”, again with a “Show” button that doesn’t show anything when clicked.

Too many uncertainties about backups. Duplicati does not seem to be reliable, I’ll have to look at Arq Backup or something, I suppose.