Try this
- Update Notification Tracker in Google Play.
- Restart your phone.
- Check your phone has some free storage.
- If App Protection is on, see "I can't unlock Notification Tracker".
- As a last step, reinstall. Create a backup first if you can still open the app.
Tell us
If it keeps happening, send us a bug report with your phone model and Android version. Crash reports help us fix it fast.