Connecting Dell Laptop to Xfinity WiFi XB7

After some issues with my previous Xfinity gear, yesterday I installed the XB7 router/gateway. The process was pretty simple. All previous settings were migrated over quite easily and we were off to the races again. In fairness there was one little resistor - the Sonos 1 - but that thing's always been a bit odd. No worries connected it via ethernet and set it up that now it works wirelessly. 

The issue showed up with my wife (enterprise) work laptop. She can see the SSID, and it appears to connect briefly ( 5-10 sec  ) and the boots her. 

Does the XB7 still support all the legacy types of WiFi modes (e.g. A, B, G) as the XB6? 

I've also  heard rumors that certain Dell laptops not being able to connect to certain channels of the router. I hope this is not the case because Xfinity has removed our ability to control this. If that is the case I'll be forced to buy 3rd party - no problem  - everyone has tons of extra cash right now. 

Any help is appreciated.