Hot reload breaks blueprints of class type when a struct containing a member of that class is defined in that class' header file.

When a struct is created in the header file for a class, and the struct contains a member that is of that class' type, performing a hot reload after changing the class will result in a Blueprint derived from that class and using that struct having compile errors. The errors can be resolved by closing and re-opening the Editor.

1. Create a new project.
2. Add a new Actor class to the project.
   • Use the name MyActor for the new class.
3. Add the following code to the header file for the new class between the #include lines and the class definition:

   class AMyActor;
   
   USTRUCT(BlueprintType)
   struct FActionData
   {
   	GENERATED_USTRUCT_BODY()
   
   	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Action Data")
   	FVector Point;
   
   	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Action Data")
   	AMyActor* Unit;
   
   	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Action Data")
   	AActor* Actor;
   };
   

4. In the class definition, add a member that is of the struct type:

   UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "TestCat")
   FActionData TheData;
   

5. Build the project in Visual Studio.
6. Open the project in the Editor.
7. Create a Blueprint that derives from MyActor.
8. In the Blueprint's Event Graph, create a setup similar to what is shown in the Works.png image.
9. Add a new UPROPERTY to the MyActor class.
10. Build the project in Visual Studio to trigger a hot reload.

RESULTS:
The build completes successfully, but the Blueprint's Event Graph now looks like the Broken.png image.

EXPECTED:
The build completes successfully and the Blueprint has no errors.

WORKAROUND:
Close and re-open the project in the Editor.