How do you prevent objects such as road pieces and houses from disappearing, I even check full lod and they still disappearing. Please Help:)

If this happens to you while in the creation kit moving around cells, hit F5 to refresh the render window. Things used to disappear on me all the time, but this always brings them back into view.

..or you can go to File > Preferences > Misc tab >Grids to load [insert number here] (put it to 25).