Android Nougat(7) and Oreo(8)

Go to your android settings and select "Battery"

Select "Battery optimization" from the top menu

Select "All apps" from the menu on the top of the list

Search from "Life Reminders" in the list and select it

Select "Don't optimize" from the dialog box

Now Life Reminders is listed as "Not optimized" and should work fine

RESTART your device after changing those settings

Here is a video to should the steps: