I'm still on LEDE Reboot 17.01.5 and want to return to 3.0.0 beta then commit the Nano upgrade. However,
sysupgrade -n /tmp/upgrade-3.0.0.bin
throws
Image metadata not found
Invalid image, hardware ID mismatch, hw:30400002 00000001 image:6d6b3531 00000001.
Image check 'platform_check_image' failed.
so what code did you run to return back to 3.0.0 beta?