Please check the possible reason and trouble shooting steps below to solve your issue:
1. The phone is powered off automatically due to low battery; please charge the phone when you see the low battery reminder;
2.Bad contact of phone battery, please reload the battery and make sure that the battery has good contact with the phone;
3. The automatic power-on/off function is turned on via phone settings, please uninstall or update the corresponding applications;
4. There are too many running applications, which cause reboot due to low memory, please terminate unused applications to ensure sufficient memory for phone operation;
5. The phone is under high load for a long time, which causes power-off due to overheat self-protection, please make sure the phone is running under allowed temperature range;
6. Loose SIM card or bad contact between SIM card and phone, please reinstall the SIM card and ensure good contact with the phone.