Xfinity modem with wifi routers

its probably because they're both in router mode and causing a double nat. You can put the orbi in access point mode. 

https://kb.netgear.com/30186/What-is-Double-NAT

Couple of options,
1. Configure the modem for transparent bridge or modem only mode. Then use the Orbi router in router mode. You'll need to contact the ISP for help and information in regards to the modem being bridged correctly.
2. If you can't bridge the modem, disable ALL wifi radios on the modem, configure the modems DMZ/ExposedHost or IP Pass-Through for the IP address the Orbi router gets from the modem. Then you can use the Orbi router in Router mode.
3. Or disable all wifi radios on the modem and connect the Orbi router to the modem, configure AP mode on the Orbi router. https://kb.netgear.com/31218/How-do-I-configure-my-Orbi-router-to-act-as-an-access-point and https://www.youtube.com/watch?v=H7LOcJ8GdDo&app=desktop
https://kb.netgear.com/26765/Disabled-Features-on-the-Router-when-set-to-AP-Mode

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lannyreese wrote:

I need two different Wi-Fi routers in my home: one to run my Ring security system without interfering with my computer Wi-Fi network. I'm using the built in router in my Xfinity Modem for connecting to the Ring products. I'm using the Orbi router to connect to my computer products. Recently, I bought an Amazon Fire Cube to enhance smart features on a dumb TV in the bedroom. It found the Xfinify Router as there is an Wi-Fi extender right next to the TV. Alexa is fussing and sending out error messages because occassionaly the Wi-Fi loses the Up load channel and Alexa is unable to correspond with its server. Comcast says that I am not allowed to use both routers at the same time as they have to time-share and can lose the proper signals from Comcast. Because of my security setup and computer setup, I don't want to have to go around and change all of the settings on the security end of the package. Any suggestions as how I can continue to use both Wi-Fi networks at the same time?

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