@Mielie I contacted Samsung and these are the trouble shooting steps that they gave me.
STEP 1:
To turn an app's notifications on or off:
1. From the home screen, swipe either up or down to access apps.
2. Select Settings.
3. Select Apps.
4. Select the application.
5. Select Notifications.
6. Select Show notifications.
STEP 2: If Step 1 did not work
Are notifications turned on for the Whatsapp? You might also want to check the lockscreen notification on your phone.
1. Go to Settings.
2. Select Lockscreen.
3. Select notification, make sure also that it is on.
4. Select notification to show.
5. Select Alert and silent notification.
STEP 3: If Step 2 did not work
The next step is to reset the app preferences on your device.
1. Go to Settings.
2. Select apps.
3. Select menu with is the three dots on the upper right corner
4. Select reset app preferences.
5. Select reset.
STEP 4: If Step 3 did not work
The next step is to enable the 'Smart pop-up view' feature for your Whatsapp.
1. Go to Settings.
2. Select advanced features.
3. Select 'Smart pop-up view'.
4. Select enable the Whatsapp.
STEP 5: if Step 4 did not work
The next step is to reset the settings of your phone.
1. Go to Settings.
2. Select General management.
3. Select Reset.
4. Select Reset all settings.
5. Select reset settings.
THESE TROUBLESHOOTING STEPS WERE FOR MY SAMSUNG NOTE10+, not sure if this will work with other devices. Contact Samsung for assurance and guidance.