Solutions:
1. Upgrade the system to the latest version.
2. After the operation of "not save" the SSID (network name), add the SSID again and enter the password using the Android keyboard.
3. Try to fill in static IP.
4. After backup,Try again after clearing the data.
5. Try to restart the router.
6. Connect to other Wi-Fi hot spots.
7. If other Wi-Fi hot spots are not available.
8. Restore the phone to the factory settings after backup. Try to reconnect without restoring the backup.
9. It is suggested to go to the after-sale center for inspection.
Notes:
WiFi failure is closely related to the router. For example, some routers may limit the MAC address or some Settings may fail after running for a long time. It is suggested to try more WiFi hot spots. If all the WiFi can not connect, it is suggested to go to the after-sale center for inspection.