In general MindBell works well without being excluded from optimizing battery use on a standard Android.
The idea of MindBell is to get a reminder from time to time throughout the day. Reminder means to wakeup the phone by the means of an alarm and play a sound, show a bell or vibrate. Waking up the phone and these actions consume battery, of course. Some energy saving mechanisms assume this to be a waste of energy and prohibit the wakeup for the sake of a longer lasting battery. Therefore it might be necessary to exclude MindBell from whatever mechanism exists on your phone.
Some Android devices - such Honor or Huawei phones - use a special user interface called EMUI. It comes with additional power saver features which prevent MindBell from working correctly. One of those is the lock screen cleanup.
These screenshots haven been taken on a Huawei P8 with Android 7.0 and Emui 5.0.3 and were kindly provided by a friendly user of MindBell. Thanks for it. I hope it will help you.
If this description does not fit to your phone, vendor, model or version please take your favourite search engine and look for something like “vendor device lock screen cleanup”, with replacing “vendor” and “device” according to your phone.
(1) Phone settings
In your phone settings open the battery settings:
(2) Battery settings
Choose to optimize those settings:
(3) Battery optimization settings
View the apps that are also running when the screen is off:
(4) Lock screen cleanup settings
Be sure MindBell is listed as an app that does not close when screen is off: