- Connect a charger to your phone, this is to bypass possible power savings mode.
- Select a different ringtone to recognise how the vibrator follows the sound.
- Check if the issue is with a specific number on incoming calls.
- Restart your phone, you should feel a vibration while the phone switches on.
Note that if you switch vibrating alert on, your phone will vibrate even if it's ringing option is set to Silent.