I only receive notifications from Whatsapp and Facebook-Messenger when I open the apps.

Open WhatsApp > Settings > Notifications >

• Message Notifications
• Group Notifications
• In-App Notifications

Check if you have not selected Non of any of the above.

On iPhone

Change alerts

To add or change an alert style for a notification:

1. Go to Settings > Notifications > Check Lock Screen [Ticked]

Change alert styles

To add or change an alert style for a notification:

1. Go to Settings > Notifications.
2. Select an app under Notification Style. 
3. Choose a type of alert and banner style. 

You can also turn sounds and badges on or off.

Change group notification settings

You can use group notifications or keep them separate.

1. Go to Settings > Notifications.
2. Select an app and tap Notification Grouping.
3. Select one of these options:

• • Automatic: Notifications from each app will appear in groups based on app alerts.
  • By App: All notifications from each app will be grouped into single expandable alerts.
  • Off: Notifications appear in the order they’re received, without grouping.

From here you can also choose how to show notification previews for specific apps. For example, you can have notification previews show up all the time or never, even when your device is locked.

Learn from here --> How do I turn push notifications on or off on Instagram ...

Watch the GIF below

Contact the app developer here --> App Support

Do you have the correct and latest version of Instagram? Watch the GIF below

If you are using the same Instagram Account on both iPhone and on iPad? Then

• How do I turn notifications on or off for someone I follow on Instagram?
• To turn notifications on or off, first go to the person's Instagram profile... See More
• I'm getting someone else's push notifications on Instagram.
• Learn what you can do if you're getting someone else's push notifications on Instagram... See More
• How do I mute push notifications on Instagram?
• You can mute push notifications on Instagram in your notification settings... See More
• How do Activity notifications work on Instagram?
• Learn more about Activity notifications on Instagram... See More
• How does Instagram process United States Digital Millennium Copyright Act (DMCA) counter-notifications?
• Learn more about how Instagram processes DMCA counter-notifications... See More
• When does Instagram send push notifications to my device?
• Learn more about when Instagram sends push notifications... See More
• How do I mute notifications from a group conversation in Instagram Direct?
• Learn how to mute notifications from a group conversation in Instagram Direct... See More
• If I've added multiple Instagram accounts, what push notifications will I get?
• Learn more about push notifications if you've added multiple Instagram accounts... See More

If everything fails contact the app developer here --> App Support or Instagram Help Center