Reminders aren’t working on my OnePlus device

Let’s try to fix this issue:

1. Open your phone's Settings.
2. Go to Battery.
3. Go to Battery optimization. 
4. Go to Not optimized apps.
5. Go to All apps.
6. Choose Flo.
7. Tap Don’t optimize.  
8. Tap Done. 
9. Go back to Settings.10. Choose Advanced.
10. Go to Recent app management. 
11. Enable Normal clear.

After that, remove Flo from the phone memory (open apps) and restart.