AIDestinationSetter is a GameObject to Entity bridge component, it expects that your FollowerEntity is not in a subscene. A* is designed to do the pathfinding in ECS land and then send the results to GameObject land.
If you want pure ECS with A*, where it’s all Entities in a Subscene, then you have to make a baker and set the DestinationPoint component using Systems or an EntityManager. This is a FollowerEntityAuthoring script I have been using for awhile that can help get you started.