What power supply are you using to power your device? Make sure that it is able to pull at least 5V and 1A. I am using a 5V 2A power supply for my AR300M.
Can you please tell me if running ‘reboot’ reboots it without causing any data loss? If you just want to shut it down, try ‘poweroff’, and then power cycle it whenever.
These would be the only ‘shutdown procedures’ that exist for OpenWRT.
It should give Linux some time to properly unmount and flush the filesystem.
If you are using EXT4 you will definitely find these commands useful, as an improper shutdown will mark your EXT4 filesystem as dirty.