I have the same problem, I was advised to try a 2D Scene Capture actor combiend with a Blueprint that can make it act like the old UDK system:
https://answers.unrealengine.com/questions/120180/creating-a-mirror-using-scene-capture-2d-actor.html
I’m still new to Blueprints so I haven’t been able to try it yet, but it look like it should work…