Please try the following:
1. Check vibration settings: go to Settings> Sound & Vibration> Vibration, and toggle on Vibrate for Calls and Notification Vibration/ Touch Feedback.
2. Press the volume key to enter the ringtone Volume Settings. Click the ringtone icon and check if the vibration switch is turned on.
3. Reboot your phone and test again.
4. Back up any important data and restore your phone to factory settings.
If the issue persists, contact the Nothing Support Team for further assistance.