Rules of the user

Why are user permissions removed after the 5.0 upgrade, and what do I need to do to do some rule control for an individual user?

I imagine you are migrating for a version older than 4.6. As explained on the 4.6 to 4.8 migration, you should define move all user defined rules to a group, as the feature of defining rules per user have been removed on version 4.8 in favor of the groups usage.

Note that this should be done manually and before the migration.