Hello. How is it possible to report a bug? As a regular user, I don't seem able to report a bug in bugs.openwrt.org.
Anyway, basically what happened is that after resetting using the command below, subsequent saves to router settings (e.g. enable WiFi, set SSID etc) were not retained. I could see it as I am applying it, but when I turn the router off and back on, it's with the default settings!!
umount /overlay && firstboot && reboot
Backkground of the issue: router was initially flashed using openwrt-18.06.1-ar71xx-generic-archer-c7-v2-squashfs-factory, then happened to do resetting from LuCI but faced some problem with firewall/interfaces settings, so thought it's best to reset using umount and firstboot, and that's when the not-retaining settings happened.
I now reflashed with openwrt-18.06.1-ar71xx-generic-archer-c7-v2-squashfs-sysupgrade and settings are saved.
Router is Archer 7 V2.