Arris S33 gigabit speed issues, upstream power low, Xfinity says it's the modem, Arris disagrees
I have an Arris s33 modem, and my download speed is capped at roughly 400 Mbps. When I first installed this modem, along with a new Wifi 6 network, I was getting regular download speeds of 800-900 Mbps. Then, after a day of no connections, and spotty internet, I am now stuck at speeds less than 400 Mbps. I have had a tech out to the house twice, they have replaced the line to my house, and have confirmed that my speed is definitly capped at 400ish Mbps with this modem. Line quality is "Excellent" according to the last tech visit. While at my house, the last tech called Xfinity while he was here, and even though my modem is "compatible" with their gigabit speeds, Xfinity said my modem was to blame for the slow speed. He said their response was to "try one of the Xfinity modems or another brand". So, I chat with Arris, and they said the upstream power levels are too low. I have one company blaming the other, and can't seem to get a straight answer as to why my speeds are so low. The modem is less than 3 months old, and other than trying another brand of modem, I don't know how to resolve this.
Upstream power levels are between 38 dBmv and 40.9. dBmv. Arris says they should be between 45 dBmV to 61 dBmV
So, is the upstream power really the issue, or is the Arris modem just not compatible with Xfinity Gig internet?