Thanks mate! This solved the issue. I really don’t understand why this is not documented.
The only thing stated in ObjectMacros.h is:
/// This function is designed to be overridden by a blueprint, but also has a native implementation.
/// Provide a body named [FunctionName]_Implementation instead of [FunctionName]; the autogenerated
/// code will include a thunk that calls the implementation method when necessary.
BlueprintNativeEvent,