The earliest recollection of this bug is traced back to PAN-OS 8.1.13 - January 09, 2024.
This bug is fixed in PAN-OS versions 9.1.2, 8.1.13.
Fixed an issue where the software pool for Regex results was depleted and caused connection failures.
For more information:
https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-release-notes/pan-os-8-1-addressed-issues/pan-os-8-1-13-addressed-issues
https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-release-notes/pan-os-9-1-addressed-issues/pan-os-9-1-2-addressed-issues