When I turn a layer into a 3D layer it disappears. If i turn draft 3D on it will reappear, or if I preComp it will reappear. continuous rasterize is not on so its not that. Active camera is set in preview window, so its not front view thing.
this is driving me nuts ... any help is welcome.
1. Make sure you are looking at the Active Camera.
2. If that doesn't fix the problem tell us more about your comp and post a screenshot with all layers showing and the u key pressed twice to show us anything you have changed in the layer properties.
You probably have a layer style applied to it or a 2D layer in your comp is breaking 3D rendering order.
Show us screenshots of your Timeline panel and Composition panel.