Adding and Interface to Blueprint that already implements a function of the Interface, fails silently and doesn't add the Interface.

Expected: Should log an error to the BP Compiler Results or (preferably) tag/convert the existing function as being an implementation of the interface and successfully add the Interface. This falls under the general ‘hard to refactor Blueprint’ topic.

I’m having the same problem.
I’m adding a function to an already implemented blueprint.
The function does not appear in the blueprints implementing the interface.
I’ve tried removing and adding the interface, and only the function appear.