Wife connection problem LG G2 (ATT)

[krant min]

I bought ATT LG G2. When I connect to home wifi, it works for 20-30 secs and then stops working. I returned it and bought new one. Its again the same.
I guess, it might be some setting either in router or in mobile. All other devices connect fine. I have N5 as well. It connects fine. But only G2.

Any settings I need to change in either router or G2?

Please help!

 

[krant min]

BTW, as specified on some other thread, I did check the firmware on my router and its up to date.