You have to parameterize the actor lists ( arrays etc ).
In the BP itself, there are spaces for all this, but unpopulated. When you drag it into the map, you can tell it what meshes you want, and the BP gets saved with that map.
When you drag it into a second map, it starts empty because you haven’t specified anything from the content browser yet. Then you can set all the parameters and let the BP populate the second map.
Does that make some sort of sense?
You could also change things at runtime, it’s just a choice you make about the design.