If you find that your iPad screen is going dark whilst using the Guided Access feature, please do the following to resolve this.
1. Exit Guided Access by triple clicking the home button and entering the pin. (*Note:* the guided access PIN may be different from the iPad lock screen PIN)
2. Update the iPad’s iOS to 12.1.1+
3. On the iPad’s home screen, touch the settings (cog) icon and go to the Generalmenu.
4. In the Accessibility > Guided Access menu, turn on the Mirror Display Auto-Locksetting down the bottom. This will mirror your Settings > Display & Brightness > Auto-Lock setting.
5. Once Guided Access re-enabled the issue will not re-occur.