Upgraded from CM600 to CM1200, upload speed halved

[maxxum23]

I figured I'd ask here before I return the new modem.

I have an xfinity 400mbps down/100mbps upload speed plan. I had been using the CM600 for a while, which gave a good 450mbps/12mbps down/up. Xfinity upgraded the infrastructure in my neighborhood and messaged me that I can get better upload as per my plan if I upgraded the modem.

I didn't do that for a while but recently they asked me to schedule a tech visit because they said they found some speed issues in my home, and indeed everything had become laggy. The tech came and changed the coax cable and connectors. The modem was CM600 till then, with 450/12 as the down/up speeds.

My router is a Netgear Nighthawk WiFi 6, mesh.

The tech suggested I upgrade to a docsis3.1 modem to get full upload bandwidth which I am paying for. I got the CM1200 which resulted in higher download speeds (650-700mbps) but the upload speed halved, and it is now 5.8 to 6mbps. 

Xfinity has reset it multiple times from their end and I have restarted it many times too. No improvement. 

I am inclined to return the CM1200 and either go back to Cm600 or try an Arris this time, unless I can get this to work.

[FURRYe38]

Has a power OFF of the modem for 1 minute then back ON been perfomed?

Speed testing with a wired PC connected to the CM1200 modem or is there a wifi router in between? 

Please post a copy and paste of the modems connection status and event log page.
https://kb.netgear.com/30007/How-do-I-obtain-the-cable-connection-information-from-a-NETGEAR-cable-m...
https://kb.netgear.com/30008/How-do-I-view-or-clear-the-event-logs-on-my-NETGEAR-cable-modem-or-mode...

Be sure your using a good quality LAN cable between the modem and router. CAT6 is recommended. 
What is the brand and model of the host wifi router connected to the modem?

[maxxum23]

I have tried the full power off, wait and restart.

The speed test is being done through the Netgear Nighthawk app, which shows the speed that the router is getting, which is cable connected to the modem. 

Testing on any other device that is connected via WiFi will of course yield lower speeds. 

Here are the logs:

Information: 

[maxxum23]

[FURRYe38]

Be sure your using a good quality LAN cable between the modem and router. CAT6 is recommended. 
What is the brand and model of the host wifi router connected to the modem?

Try Speed testing with a wired PC connected to the CM1200 modem with out a wifi router in between.

Any Criticals, Errors or Warnings seen in the event logs needs to be reviewed and resolved by the ISP. Indicates a signal issue on the ISP line up to the modem. Otherwise cable connection data looks good. Power levels are good as well. 

[maxxum23]

The router is Netgear Nighthawk mesh WiFi 6

[plemans]

I'd return it and get either a coda56 or wait and get the CM3000 when its released. those will both support xfinity's "next gen" speeds and you'll get the faster 100mbps upload. The CM1200 isn't currently on that list and I haven't heard anything about it being worked on yet. 

[plemans]

Their list of supported devices for next gen speeds can be found here: 

knowledgebase/next-generation-internet - Comcast_Xfinity (reddit.com)

Plus I think the coda56 is cheaper. 

[maxxum23]

Yes. This one is going right back.

FWIW I connected a laptop directly using a cable to the modem and tested it. The upload is still under 6mbps.

[maxxum23]

Back to the old modem CM6900 (docsis 3.0). Unfortunately the old upload speed of 12mbps was no longer available, and now this one also gets only 6mbps. It has to do with Xfinity but they will charge for every visit they make, because I am not renting equipment from them. Perhaps a change in provider is in order.

[FURRYe38]

IF you have that option, something to explore.

[Kitsap]

Additional information on Xfinity with the CODA and CODA56 modems can be found here:

https://www.dslreports.com/forum/r33821305-Equip-Xfinity-customers-with-CODA-CODA56-modems