@JoseCortijo - I got my issue resolved with the help of PAN support, figured I'd share it here in case it helps you. For my two LDAP server profiles, i nstead of using LDAP/636 to each of my AD domains (root and child), I switched to GlobalCatalog/3269 to the root domain as well as LDAP/636 to the root domain. I then changed User ID group mapping to use the GlobalCatalog server profile, so that it could read all domains, and blanked the User Domain field in the group mapping config. Next, I added the relevant AD groups to the Group Mapping Group Include list and also to the SAML Authentication Profile Allow List under Advanced. Now in my Agent Client Settings, I add the relevant groups to the Source User list.
Here is the doc that helped me, as it recommends using Global Catalog if you have Universal AD Groups, and also mentions that the User Domain field can usually be left blank in the Group Mapping config: https://docs.paloaltonetworks.com/pan-os/10-2/pan-os-admin/user-id/map-users-to-groups
HTH!
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