The earliest recollection of this bug is traced back to PAN-OS 9.1.8 - July 29, 2024. This bug is fixed in PAN-OS versions 9.1.8. Fixed an issue where editing device log forwarding in the collector group then filtering specific firewalls and adding new firewalls caused the old firewalls to disappear from the log forwarding preferences list. For more information: https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-release-notes/pan-os-9-1-addressed-issues/pan-os-9-1-8-addressed-issues