After updating a project to 4.16, I found an error in the main HUD widget. Unable to Create Template for Widget. Fast Create Widget Warning! This class cannot be created using the fast path, because the property Hero2 on Master_GameHUD_Widget_C references Hero2. Please add the ‘Instanced’ flag to …

I had this error too because I copy-pasted user widgets. When I dragged them in 1 by 1 I was able to compile.