I've just bought a used archer c59 v1 eu and have installed OpenWRT 18.06.2.
I realized, that there is no radio1 interface on the overview page and I don't even find any footprint of ath10k in the output of dmesg.
It came to my mind that 5G radio was not even clickable with original firmware. Is it possible that 5Ghz part of this router is gone? How could I proof this?
If one of the radios won't work with official firmware from the manufacturer, either the hardware has failed or the ART partition is corrupted. Either way you should seek to get your money back.