Welcome to the forum @Nordlicht
FreeNAS 11.3 U1 - password resetting might help, especially if you saw those Post Install Notes.
Duplicati.Server.exe shows option third-party plugin you are running is probably using each start.
You can probably use your ps command with the correct options to see the options Duplicati got.
--webservice-password
The password required to access the webserver. This option is saved so you do not need to set it on each run. Setting an empty value disables the password.
If you like to use Settings to change the password (which is the way Duplicati ships it), avoid that.
Other Google search references that may or may not apply:
Duplicati Plugin for System Backup to Google Drive (someone did a cat PLUGIN_INFO to check)
https://github.com/rexit1982/iocage-plugin-duplicati/blob/master/overlay/usr/local/etc/rc.d/duplicati
is source for a start script, however I don’t know if it’s yours.
Note that TrueNAS CORE, being FreeBSD, won’t run a future version of Duplicati. SCALE should.
This won’t be an immediate problem, and possibly .NET will be ported to FreeBSD by that version.