If you have more than one monitor and switch their placement around, you may find that when that app is started, it is shown outside the monitor's visible area.
There are 2 ways to make it come back to the visible area:
- Using the 'move' option
Use Alt-Tab to select the app
press Alt-space, M and then use the left/right keys to bring it into view
- Use this neat little utility, called borderline