On my wife's galaxy s5 the bar on the top that shows the time and battery percentage dissappears unless she opens up an app. Any thoughts on how to stop this?
Sounds like something is seriously wonky with android. It may be an app causing this issue. The simplest way to fix this would be to backup all data to the computer using samsung smartswitch and factory reset the phone through the bootloader.
There may be a simpler solution but what im describing is a more sure way of resolving the issue. Good luck!
Welcome to Android Central! Does she have any alternate launchers installed, like Nova Launcher? Does this happen in Safe Mode as well? https://support.t-mobile.com/docs/DOC-28456