Pretty sure it can be that way since my phone developed the same problem in the last week.
The Messages app displays the badge correctly, but the sound, banner, lock screen, and notification centre notifications have all ceased.
Naturally, I have checked my notifications settings and all is in order according to those.
It can be hard to tell what the specific conditions of the phone are when this happens as, you know, I’m not getting the notifications, but looking at the received message times tells me that it happens regardless of:
- Locked/unlocked
- Silent mode on/off
- Messages app being open/closed
- Sender of message
At the time the issue started, a system update had been recently completed.
Not long after the update, I had changed the system time/date as well (to a point that turned out prior to the latest three conversations I had sent/received messages in). The time/date has since been correctly reverted through reactivating the “Set Automatically” option.
iMessage was also switched off in Settings around this time since I do not use the feature and got continuous login requests from it despite entering my details, and even requests to log in to my sister’s account which had been used only once (and very briefly) in the App Store on the device before switching back to my account.
EDIT: Phone model is iPhone 6S Plus
