I have experienced and not found a solution as to why the UI elements rendered in “world space” are disappearing.
The canvas (and their dependent UI objects like buttons, etc) disappear when played in the world space setting and when previewed in the “game” window/view of Unity. When the objects are edited, they appear but when the game window/view is selected, the objects disappear again.
Has anyone found a work-around for this or a solution. I heard switching to the new version of Unity would work from 5.3.5.f1 to 5.3.6.f1, but it did not.