Connection issues following xFi Advantage gateway / gigabit upgrade

I've read through the various connection issue questions posted here, but there's nothing quite like the problem I'm experiencing. Last week, I upgraded from 300 Mbps Blast service on my client-owned Aaris modem to gigabit service using a new, xFinity supplied xFi Advanced gateway. Since activating the new gateway, I've experienced a whole host of problems. First, it will randomly lose connection. It has never stayed connected for more than about 36 hours without cutting off all internet and phone access at some point. The gateway has to be power cycled to fix this, but it does come back following reboot. Second, none of my Amazon Echo devices will connect to the xFi wifi. I tried both 5 GHz and 2.4 GHz bands, and I even renamed the SSIDs and reset the passwords to match my previouls router thinking that would make the change seamless to the Echos, but they all refuse to connect to wifi, even after trying to use the Alexa app to reconnect or doing a factory reset on the Echo. And, finally, some websites do not load at all on some devices, either using a wired or wireless connection. For example, my son's MacBook Air will connect to Google and YouTube, but not Outlook.com to get his mail, with the results unchanged on wifi or wired connection. My phone is similar - sites like CNN.com are fine, but I can;t get to my Outlook email. But my son's Win 10 desktop computer and my own Win 10 laptop seem to have no problems, wither on wifi or wired. Very frustrated at this point. I even tried reconnecting my old router, a TP-Link Archer C3200, after putting the xFi gateway in bridge mode, but the router shows no internet connection on either of the xFi gateway ports. Extremely frustrated at this point, and tech support can only seem to offer resetting the gateway as a solution. Any ideas?