I have currently OpenWrt 21.02.0-rc3, r16172-2aba3e9784 running on my Pi4b I upgraded to this from a snapshot by building with the image builder. I was trying to avoid doing that now we have an official release by using sysupgrade and keeping the settings. However, after flashing and the reboot the version has not changed so it tries obviously then fails. I wanted to hang to the configuration rather than the bare image without the USB dongle driver etc.
I can build from scratch again of course but ideally I'd like to resolve this so in the future I can do it easily. Any thoughts as to where to look to see what is going wrong?
It's more making sure I have the driver for the USB, everything else as you say can be readded but without internet access not. I've just built a package. I'll try and update using that later but cannot now, got to go out in an hour.
In the end what worked was making a list of all the packages I had installed. Adding them to the image build, copying that full image to a spare card. The opening the saved configuration and copying it to the newly flashed card.. That installed and let me login, then restored the configuration.