Please try the following:
1. Remove the phone case if using a metal one.
2. Avoid places with dense crowds or poor signal.
3. Replace the SIM card to see if the issue is with the phone or SIM card.
4. Turn Airplane Mode off and on to see if the signal goes back to normal.
5. Check if the phone's system is up to date. If not, update it to the latest one and see if this improves the signal.
If the issue persists, contact the Nothing Support Team for further assistance.