I have been trying to install OpenWRT on Malaysian Unifi Archer C1200 v1 using OpenWRT. It did not work when I use Firmware Upgrade feature of the stock firmware, it gives me "Unable to Upgrade" error. However I managed to upgrade it to EU and US version but even installing from the EU and US version won't work. I also tried to install old LEDE version but nothing seems to work.
I managed to install 1.1.0 Build 20170413 rel.56876 (US) and 1.1.3 Build 20180502 rel.46288_2018-05-02_13.47.59 (EU).
The one still fails is openwrt-18.06.4-ar71xx-generic-archer-c5-v1-squashfs-factory.bin