Oh I was questioned why to ditch the logfile: directive when diagnosing.
There is no log-rotate in place/configured to maintain and archive the log file.
It will just keep on growing until the filesystem is full.
Also its impractical to diagnose if the filesize is too large.
Think about greping or browsing with less.
If no logfile: is specified, everything gets logged by the systemd-journald.service which can be queried with the journalctl command.
The journal size is maintained by this service.
And if you up verbosity to three minimal in the Unbound config file, you can see individual queries in the journal and how they are processed ... for diagnosing.