If a scenario uses a custom POI with the same epb name as an existing POI in the game prefabs folder, it should ALWAYS take priority and override the file in the Prefabs folder (NO EXCEPTIONS). If you attach a story mission to an updated POI for the scenario, the game will still be able to spawn the prefab folder one breaking any and all attached missions. Basically, unless every single playfield entry is added and altered using a unique name, unwanted POIs will continue to spawn. This should obviously be changed.