LG G2 causing internet dropping connection

I have got same issue on EE BrightBox. When I use my old TalkTalk router all is OK. So it is BrightBox and it drops connection only when G2 coming up online.
 
Sorry for my bad English. I found a solution to the problem at its LG G2 Verizon. WiFi reconnected my phone when I was searching for a cell network. Remove your SIM card and test your WiFi connection.