Hi Phelps,
- Please try resetting your network settings and try again. (Settings > System > Advanced > Reset options > Reset Wi-Fi, mobile & Bluetooth)
- Please tell me your mobile network provider.
- Please change to another SIM card by another network provider, and check if the problem still appears.
Please also put your SIM card into other phones and check if the problem appears.
- Please show me a screenshot of the signal strength when the problem appears.
(Settings > System > About phone > SIM status)
Thank you 🙂