Hi,
i made a backup with LUCI on my main-router (FritzBox 4040 OpenWrt 19.07.3 r11063-85e04e9f46) and restored this with LUCI to an other 4040 with 19.07.7
The restore runs without error and the system reboots. After reboot there are no changes, the backup is not restored. Only the root password is restored from the backup
I have already done a factory-reset.
Then I made a small change (changed the hostname via LUCI) an made a reboot. The hostname is stored.
After that I tried the restore again. result, the Hostname is default (openwrt) and not the changed one before or the one from the backup.
The backup is a simple .tar.gz file.
You can easily look into its contents in your PC (with winrar, 7zip, whatever) and verify that is has the expected contents (config files etc.)
And you can move it to your router with scp (winscp etc.) and extract the contents there.
You should look at the logs. Possibly you have too full flash, or something like that, and the flash rootfs (overlay) is not enabled, and all your changes go to RAM overlay that naturally gets wiped at reboot.
That is the failing router, right?
have you opkg installed the possible add-on packages that your config might depend on? Do you have any special config, or just the default packages?
Backups generally work for the same or a newer OpenWrt version, assuming that you have installed all needed packages. The backup only stores config, but does not restore the possbile add-on packages that you have installed.
OpenWrt is not really designed for that, but some alternatives:
Build personalised OpenWrt images for your devices, so that all your devices XYZ have the same packages. Then it is easy to copy settings via backup.
The file system is usually built around the concept of "flashed firmware as /rom" + "r/w overlay as /overlay" shown together as the root filesystem "/" via the overlayfs. All settings and the add-on packages that you installed, are there in /overlay/upper.
That enables you to .tar.gz archive everything in /overlay/upper in one device and restore it into /overlay/upper another router, assuming that the devices are identical and have have the same flashed firmware versions. After restoring the archive, you should reboot so that the router can boot with your restored packages.
(Note that this does not apply to the SD card base systems and similar, which are without overlay)