Keep iPad always on and locked to one app. In >iOS 12 Ive got an iPad mini 4 in a wall mount like this here.

I want to set the iPad screen to be constantly on, locked to one app. Prior to iOS 12 i was able to do this by A) setting the sleep setting to "never" and B) putting the iPad into guided access mode to lock it into one app. But since the release of iOS 12 the iPad will only stay on for about 30 minutes, with settings A) and B). If i just set the iPad to setting A) it will stay on indefinitely, but i cant lock the screen to a single app. For more info on this issue, see this thread here. 

Is there another way to lock an iPad to a single app, whilst at the same time keeping the screen on indefinitely ? Perhaps through adopting the iPad into MDM mode or developer mode ?
I have seen several people with the same issue. Assuming you upgraded the iPad with guided access enabled follow these steps:


  I have found that if Guided access was enabled prior to the upgrade it
  might reset in this process.
  
  
  Turn off Guided Access in Accessibility / Settings.
  Hard reboot.  (Hold Home and Lock buttons for 7 seconds)
  Turn on Guided Access in Accessibility / Settings.  Reset Passcode.
  




From Kiosk:


  iOS 12.1.1 has been released and includes a fix to this issue, but requires a change to a new setting introduced in this release to prevent the screen from sleeping: General > Accessibility > Guided Access > Mirror Display Auto-Lock > ON.  


to update your device, go to Settings -> General -> Software Update