When you upgrade to a Panorama 8.0 (or later) release, Panorama
Log Collectors use a new log storage format. Because Panorama can
no longer generate reports or ACC data from logs in the pre-8.0-release log
format, you must migrate the existing logs as soon as you upgrade Panorama
and its Log Collectors from a PAN-OS 7.1 or earlier release to a PAN-OS
8.0 or later release. Log migration is a one-time task; after you
migrate the logs on the Log Collector as part an upgrade to a PAN-OS
8.0 or later release, you do not need to migrate them again.