This is currently a problem with intellisense in Visual Studio using 4.20. Any class that uses the GENERATED_CLASS_BODY macro seems to be affected.
The difference between GENERATED_UCLASS_BODY and GENERATED_BODY is that the former sets accessibility to public afterwards, whereas the latter sets it to be private. Visual Studio 2017, even with Visual Assist installed, seems to miss the reset to public accessibility afterwards and reports accessing those members or functions as an error when in actuality they are available (as noted by the successful build).