RE: Apple TV and Rachio unable to connect

I have a Rachio controller that will not connect to the Rachio server although it will connect to my 2.4 g network still. I’ve tried everything over which I have control and no joy. It will connect through a phone hotspot. I suspect a setting on the Xfinity side is the issue and my owned router is less than two years old and gets good speed. It’s an. Arris t25 which is now listed as compatible but not recommended. The only voice recommended modem is the netgear cm2050v which is 300$ and I really do not want to spend that much just to get one smart device working. Any suggestions?