[Zubersoft]

When you say the screen turns off, does that mean everything on the entire screen goes black, or are you just seeing some parts of the application as being black? The reason I ask is that MobileSheets does not have the ability to turn on and off the screen, so even though you aren't seeing this with other applications, it still sounds like some kind of hardware issue to me. It may just be by chance that you haven't seen it with other applications. If you go to Settings->Display Settings and uncheck the "Fullscreen mode" option and ensure the "Hide the navigation bar" setting is also disabled, do you still encounter the issue? If you go to Settings->Other Settings->Keep Screen On, have you tried turning that to "Disable" to see if that fixes the issue? Those are the only three settings related to the screen, so it's worth checking if the problem goes away when they are all turned off.

Mike