So most likely you saw this post too:
Making widget component stay above rotating actor? - #8 by Everynone
I’m a bit lost myself now, can’t think of any reason why the component would not follow a component it is attached to. You should comment the PostEditMove override to at least not modify things during an editor event, then put breakpoints within
WidgetComponent->SetupAttachment(MeshComponent);
to see if attachment is done properly.
If you don’t see anything obvious temporarily replace the widget component with a mesh in the constructor and see if that behaves properly. If so, the problem lies within the widget component.