You saw the notification, then it was gone. Before blaming the app, know that Android itself is usually the culprit. Here is what is happening and what to do.
The real reasons
1. Notification limits (Android 12+)
Newer Android versions cap how many notifications an app can show at once. Once the limit is hit, older ones are silently removed.
2. Battery optimization
Manufacturers aggressively kill background work. If the source app is "optimized," its notifications may not arrive or may be cleared.
3. Do Not Disturb / routines
A DND schedule or a custom routine can auto-dismiss or hide notifications without you noticing.
4. "Auto-clean" in some launchers
Some OEM launchers clear the shade after a timeout or on lock.
Fixes that actually work
- Set the important app to Unrestricted battery usage (Settings → Apps → Battery).
- Turn off any launcher "auto-clear notifications" option.
- Check DND rules and remove auto-dismiss routines.
- On Android 11+, enable Notification history to at least recover what vanished.
A simpler fix: pin what matters
System tweaks help, but the durable fix is to stop relying on the volatile shade. With Pinnit, you pin the notification you care about and it stays at the top regardless of limits, reboots of the list, or new arrivals. Pair it with Android's notification history and you essentially stop losing things.