Invisible sides

Actually I was using 4.12.5 and then this thing happened and I updated to lastest verison of ue4 for now (It must be 4.14). My problem is when I ‘‘add’’ a geometry like a block, it becomes invisible. And also when I copy and paste a block same thing happens. I don’t know what to do and also I am not sure that it is a bug. When I build the lighting I can see these invisible blocks, they are turning to normal but when I add again, bug happens

][1]

thanks

Closing as Duplicate of Invisible Sides - Community & Industry Discussion - Epic Developer Community Forums