Netgear WiFi Range Extender EX6100v2 can't connect to Wifi from Router Arris NVG468MQ

I just switch my internet carrier from Spectrum to Frontier Fios. I has used my Wifi extender EX6100v2 with Spectrum for almost 2 years now. However, when I switch to Frontier Fios, the Wifi extender can't connect to the Wifi any more. I tried to put the Wifi extender next to the router but it couldn't recognize the Wifi signal either. 

I switched the mode to Access point and connected the extender to router using a Ethernet cable, and it worked. But when I switched the mode back to Extender, it didn't work again. 

I factory reseted the extender couple times but it did't help either.

My current router model is Arris NVG468MQ.

Is there any suggesstion to fix this problem? Thank you.