on UE4 version 16.3 and VS 2017 when I open any header file with VS i get the same results as the OP: when added a new line or deleted one, random errors about UCLASS show up. I will try it with UE4 17 when I can. However my point is that the accepted answer being “we’ve not heard you etc etc” is not cool. If this were stackoverflow you would have gotten lots of negative points. Think about it this way: what should visitors see marked as answer when they come to the page?: The exact post that resolves the issue. if issue is resolved in comments instead, I urge you to update your answer to include the resolution, that way you would have a better documented forum with higher quality content.