iPhone 12 text alert not sounding intermittently

Hello JohnJE1957,

Thanks for verifying that information.

Is it specific threads? Mute only that one thread is possible, and multiple threads or even contacts can be muted. Check for a crescent moon on contacts, or specific threads:

Use Messages on your iPhone or iPad - Apple Support

"Turn on Hide Alerts

1. Open Messages.
2. Swipe left over the conversation that you want to mute.
3. Tap the Alerts button .

• When Hide Alerts is on, the Alerts button  appears next to the conversation. This stops notifications only for that conversation, not your device. You’ll still receive all other messages and see notifications for them on your Lock Screen."

If these steps do not help, please contact Apple Support to investigate this further: Apple Support

Thanks.

Hello JohnJE1957,

To help us get a better understanding of the issue, we’d like to ask a few questions.

1. Does the issue only happen with notifications for the Messages app, or do you experience issues with notifications for other apps as well?

2. You mentioned that the notification sound doesn't play; do you receive badge or banner notifications successfully?

That information will help us plan how to proceed.

Please also check out the following link, which will guide you through how to review and manage notification settings, which may help: Change notification settings on iPhone

Change notification settings on iPhone

In Settings , choose which apps can send notifications, change the alert sound, set up location-based alerts, allow government alerts, and more.

Change notification settings

Most notification settings can be customized for each app. You can turn app notifications on or off, have notifications play a sound, choose how and where you want app notifications to appear when your device is unlocked, and more.

1. Go to Settings  > Notifications.

2. Choose how you want notifications displayed on the Lock Screen:

• View just the number of notifications: Tap Count.

• View the notifications grouped into stacks by app: Tap Stack.

• View the notifications in a list: Tap List.

When notifications arrive, you can change the layout by pinching the notifications on the Lock Screen.

3. To schedule a notifications summary, tap Scheduled Summary, then turn on Scheduled Summary.

Select the apps you want notifications for in your summary, set a time for delivery of your summary, then tap  at the top left. (See schedule a notifications summary.)

4. To choose when you want notification previews to appear, tap Show Previews, select an option—Always, When Unlocked, or Never—then tap  at the top left.

Previews can include things like text (from Messages and Mail) and invitation details (from Calendar). You can override this setting for individual apps.

5. Tap an app below Notification Style, then turn Allow Notifications on or off.

If you turn on Allow Notifications, choose when you want the notifications delivered—immediately or in the scheduled notifications summary—and turn Time Sensitive Notifications on or off.

For many apps, you can also set a notification banner style and turn sounds and badges on or off.

6. Tap Notification Grouping, then choose how you want the notifications grouped:

• Automatic: The notifications from the app are grouped according to organizing criteria within the app, such as by topic or thread.

• By App: All the notifications from the app are grouped together.

• Off: Turn off grouping.

To turn off notifications selectively for apps, go to Settings > Notifications > Siri Suggestions, then turn off any app.

When you use Focus, it delays the delivery of notifications on iPhone to prevent interruptions. You can schedule a time to receive a summary of the notifications you missed. See Schedule a notification summary.

Thanks!