In XU 2.x, Windows AD users could be assigend to custom user groups. This is no longer possible in XU 3.x. This is a breaking change as opposed to XU 2.x.
As a consequence, Windows AD users, that had been assigned to custom user groups in XU 2.x will no longer be assigned to these groups when migrating to XU 3.x.
Security will not be affected but will be broken down to user level, as those users will be removed from the custom groups during the migration process.