Just got the Oreo update. Now get alerted every time mobile service drops out. Intensely annoying on trains, in buildings, etc etc.
- Go to Settings.
- Select Apps and Notifications.
- Press see all apps.
- Press the three dots at the top and select Show System.
- Scroll down to Android System and select.
- Tap Notifications.
- Scroll down to Network Status and hit that. I suggest set to low so you are not notified at all.