Here is an update of this issue that I had.
I did reverted back to the 4.3 yesterday and the hotspot was working fine.
and upgraded again to 4.4.2 and flash the FTF for c6502 again, exactly the same one I've used before.
and guess what happened this morning after I replied previous post. I've turn on the hotspot, and it works fine.
Reboot it once one hour ago and hotspot still working fine.
Maybe something went wrong from my initial upgrade.