Hi community,
I had the same issues and found this thread.
With the latest version (4.24) I had to use USTRUCT(BlueprintType) and UPROPERTY(BlueprintReadWrite,…) to make it breakable. Furthermore you can use UPROPERTY(EditAnywhere, BlueprintReadWrite,…) to make it breakable and editable in the editor. I use these properties to set animations and use them in the Blueprint animation script.