I got the same issue. You need to reflash the stock Android and execute the OTA update once only.
A few post before, you have a download link to get all the tools and the ROM image as well as a PDF guide.
On my side, i have a Asus RT-AC87U router which is probably one of the best available so far. Compare to my Cube Talk 9X U65GT, the Wifi of my Teclast X98 plus 2 C2D6 is really crap.
I wonder if someone already tried to fix the antenna inside or so ?