I hope I understand your problem correctly, I’m pretty new to blueprints as well so if I get it wrong, my apologies.
I think this: " assigned in both blueprints" is where you might have gone wrong?
Interfaces aren’t like “bridges” that connect things. They are more like “classes” but they don’t have their own implementation.
So if you have BP A and BP B
and A wants to get something from B without knowing the exact class of B you can create a interface called “C”
A still needs to find a reference to B somehow. Maybe by colliding with it, searching for nearby actors or stuff like that. And then when you have the reference you can then assume it’s of interface “C” and use it as if it was.
I hope that helps a bit. I don’t want to explain to much in case I misunderstood you.