The latest firmware version for Huawei B683 available in 2021 is:

Power interruption or incompatible config. Solution: Perform a hardware factory reset: Unplug, wait 30 sec, plug in while holding reset button for 20 seconds until LEDs flash rapidly. Then try reflashing.

Newer 5G-ready SIM cards sometimes have compatibility issues with 2019-era firmware. A 2021 update improves USIM application processing and APN auto-detection.