On certain devices, Android kills apps and does not allow them to restart automatically. That can cause ZenScreen to not track time or display block screen reliably.
Please tap on your device manufacturers logo and follow the important steps mentioned there to ensure that ZenScreen can work reliably.
If your device manufacturer is not listed below, please follow generic directions at the bottom of this page.
General Directions for Other Devices:
Go to device Settings and find the permission that allows ZenScreen to auto-restart. This is typically under the following places:
Settings > Apps > ZenScreen
Settings > Battery
Settings > Battery & Performance