I did yes. I also tried again on an empty project and it’s definitely busted on my side. This has happened many times to me. I’ve attached two images showing what happens when you change an already implemented function (ie with an output or else it’d not implement as a function in its own graph on the blueprint) to not have an output - it remains implemented as a function yet the colour changes to yellow… but it’s now not implemented the same as had it not had an output to begin with.
Are you sure you added an output to the interface function, then implemented that function inside a blueprint, then go back to the interface and remove the output? After you do that it should still be implemented as a function, not as an event (as it should be if you don’t have an output).
As you can tell from the image the two interface calls have the same colour and should be called in the same way…