XB7 - Double NAT, bridge mode, dropping connections

I'm going to drop all our fav topics in the same thread. I've researched so many threads going back to 2016 talking about each of these issues but no solution has been working for me because they kinda work in combination for me. 

My setup: I use the Xfinity modem but use an Airport Extreme as a router. No other wired connection to the modem. 

I've had Xfinity for a little over 2years with the modem in bridge mode. I just got upgraded to an XB7 (with one port marked with the orange mark). At first, the router was connected to one of the non-orange marking ports. I put the XB7 in Bridge mode and the internet kept dropping every 5 mins, even though the router showed a live connection (green light). I put the XB7 back into transmission WiFi mode and the internet is stable although the Airport Extreme now throws Double NAT errors. Even if I ignore the Double NAT error, my Plex absolutely does not like it and its remote connection is in jeopardy. So, I want to solve this out. 

I have also tried checking the box on making the Port 2 as Xfinity Home Network but that doesn't work either. The orange mark on my XB7 is Port 4. I have also tried all these solutions with the router on Port 4 as well but no dice. 

So, any tips?