The earliest recollection of this bug is traced back to PAN-OS 8.1.15 - January 09, 2024.
This bug is fixed in PAN-OS versions 8.1.15.
Fixed an issue where scheduled reports did not run on a PA-7000 Series firewall not managed by Panorama after upgrade to 8.1.10 or 9.0.4 and later versions.
For more information:
https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-release-notes/pan-os-8-1-addressed-issues/pan-os-8-1-15-addressed-issues