In AEM6.1 and later versions, there are system users that are included with AEM out of the box. The users already have ACLs created under various paths such as /apps, /libs, /etc, /var, /content. and some of the subpaths. If ACLs are accidentally overwritten during a data migration from an older AEM version to a newer one, they can break various features in AEM.
The /apps, /etc/clientlibs, /var/clientlibs, and /libs path ACLs are if overwritten, can break AEM:
- Client library overlay files under /apps do not work.
- The div tags which are generated around components do not show up
- Other issues such as broken user interface, authentication.
The clientlibs-service user and other users are missing their access to the previously mentioned paths.