Shaun, make sure that there is not a red box at the top left of your screen. If there is then anything you are working on is not saved. Saved work occurs as you work on things and if you are not currently connected then it cannot save whatever you are working on.
However, assuming that you are connected:
Map items and character tokens should not vanish if they were there. However, as Quatar said, sometimes another object on that layer will cover them up.
This should not occur either but it is more likely.
If none of this helps, let us know.
- Gauss