When adding a blueprint interface to child actors, you may run into a situation where you add new inputs to one of the blueprint interface functions that has already been implemented in the event graph of an actor actor, and when you go to compile, your met with this error, [Cannot override interface which is declared in a parent with a different signature]. I’m unsure of what causes the bug, but it only effects blueprints that are children of other blueprints, an easy fix is to delete the implemented event node from the child actor, go to the parent actor, implement the function there, compile the parent, then delete the node from the parent and reimplement it back on the child. This should solve the issue.