Hardware minor issue
I'd this problem almost two weeks b4. Originally my wifi was very good but one day (two weeks ago) I found my wifi signal weaken and I at first thought that was a software issue because I flash my rom frequently. After that I flashed back the original and even used OTA upgrade. However, nothing helped and the wifi reception was still weak.
Today, I boldly disassemble the back cover of the One X and tested there was a two contact pts that touching the back cover anntena (near the volume adjusting button). I tried using a metal strip to link the two contac pts together and check with wifi analyzer and I found the reception back to very strong. So I'm sure it is contact problem, so I clean all the contact pts and make sure all contacts are good enough to touch the back cover anntena by lifting the contact pts a bit higher.
Now I'm back to my original wifi reception power happily. But one thing, open the back is not easy and sure will give you some scrathes!