When I was testing, I just used the GUI Services: Unbound DNS: Blacklist and hit the Save button to manually update DNSBL.I'm logging-in to the GUI using root and I have no problem creating cron entries in System: Settings: CronI selected Download Unbound DNSBLs and restart. I run it early each morning.After you Save and Apply, login to the shell and look at /var/cron/tabs/nobody. See if there's an entry for executing "/usr/local/sbin/configctl unbound dnsbl" (or maybe unboundplus depending on which "Download Unbound DNSBLs and restart" you selected in the GUI.
Do you have two Download Unbound entries? When I look at what they actually enter into cron one is for Unbound and one is for UnboundPlus.
Can you tick enable and apply several times?