The earliest recollection of this bug is traced back to PAN-OS 9.1.10 - July 29, 2024.
This bug is fixed in PAN-OS versions 9.1.10.
Fixed an issue where using XML special characters in the Uninstalled GlobalProtect APP password in the application configuration ( Networks > GlobalProtect > Portals > Agent > App ) disrupted portal connectivity.
For more information:
https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-release-notes/pan-os-9-1-addressed-issues/pan-os-9-1-10-addressed-issues