Word preview Everywhere

I’m working on the design of a city but I have a word preview in everywhere I do not know what to make it disappear I am also new in UE4 any help ?

This preview is indicate that linghtmap and shadow was not built. If you want to make them disapear just click Build arrow down and build only lights and after your pc made the calculation preview disapear.
PS: any big change on your objects make appear again this think