The firmware contains a persistent client. This is the "phone home" agent. Every few minutes, the device pings the ISP's ACS (Auto Configuration Server). If the server detects that you have disabled Wi-Fi, changed the super admin password, or enabled bridge mode, it will silently push a "Corrective Configuration" overwriting your changes.
This is the safest method as it pulls the official version directly from the update server. Ratr/docs/Huawei-DG8245V-10-Config.md at main - GitHub Huawei Dg8245v-10 Firmware
Can you run OpenWrt on the DG8245V-10?