public static event Action<PackageRegistrationEventArgs> registeredPackages

Occurs after the asset database is done refreshing, which is after scripts are compiled and the Domain reloaded (if necessary). When you add, update, or remove a package that contains code, a Domain Reload occurs, which resets registered event handlers. To ensure that your event handler is called, use InitializeOnLoadAttribute or InitializeOnLoadMethodAttribute to register the event handler after the Domain Reload occurs but before the event is raised. Note: There is no guarantee that the AssetPostprocessor will finish by the time this event is raised, so don't rely on the execution order for post-processing events.