I think there is some misunderstanding about factory and sysupgrade firmware.

For these routers, there is no “factory” firmware. If you have your own sysupgrade firmware with all of your config compiled in, after you flash it to the router, the router’s firmware will be replaced. If you press the router button for 10 seconds and it will reset to your firmware only. The old firmware will never come back because it is erased.

I think your problem is that you didn’t replace the firmware with your firmware or your firmware don’t have your config compiled in. You should put these config in your [openwrt]/files/ when you compile your firmware.

Also please let me know what is the model of your Huawei LTE dongle. Are you compiled your firmware based on Trunk? How you compiled your firmware.