I’ve had the same problem. I think in my case it occurred because I was accessing private variables from the cpp class directly from the blueprint via the BlueprintReadWrite macro. I made those variables truly private and removed any UPROPERTY macros, instead, I set up public getter functions with UFUNCTION(BlueprintCallable) macros, and access the functions thru those getter functions. Now I can call them right after I compile cpp files, without having to compile blueprints again. And in general, exposing the private variables of a class thru getter and setter functions is better coding practice anyways.