The earliest recollection of this bug is traced back to PAN-OS 9.1 - July 22, 2025. This issue is now resolved. See PAN-OS 9.1.9 Addressed Issues. GlobalProtect clients in systems with umlaut diacritics in the serial number are unable to log in to the GlobalProtect gateway. For more information: https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-release-notes/pan-os-9-1-release-information/known-issues/known-issues-related-to-pan-os-9-1-releases https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-release-notes/pan-os-9-1-release-information/known-issues/known-issues-related-to-pan-os-9-1-releases/pan-os-9-1-6-known-issues https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-release-notes/pan-os-9-1-release-information/known-issues/known-issues-related-to-pan-os-9-1-releases/pan-os-9-1-7-known-issues https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-release-notes/pan-os-9-1-release-information/known-issues/known-issues-related-to-pan-os-9-1-releases/pan-os-9-1-8-known-issues https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-release-notes/pan-os-9-1-release-information/known-issues/known-issues-related-to-pan-os-9-1-releases/pan-os-9-1-9-known-issues