Slow, dropped, and unstable connection, after new modem/router and upgrading speed/plan.

Hi and thanks for any assistance. I hope this helps narrow it down. I did notice that the CMTS during the SYNC timing failures come up as all 00:00

I apologize, I forgot to answer that. I'm on the 2,000 plan.

I checked and it looks like it's just old/junk cable from everything I could find, there is at least one splice (corrosion and oxidized), and there must be splitters hidden in the old attic space that I cannot access. There is a short (+/- 3ft.) run from the drop/box that enters the attic and I found two outlet/receptacle boxes with coax cables inside the house (covered with blank plates). The only coax cable in use is at the complete opposite end of the house (over 100' away, even when run through the old attic space) from the drop/box.

Please let me know if this makes sense as the best/easiest option that you think should/would work and hopefully fix the problem(s). My plan is to relocate the modem/router to the end of the house where the drop/box is located, run a new RG6 cable +/- 10ft (Cimple Co has good reviews and their RG6 is swept 3.0GHz [2.3-3000MHz], 75Ohm) since there is only 1 device that actually requires an Ethernet port. A few other devices were plugged in (TV, gaming device, & lighting controls), just because the ports were right there/available, but those devices are all WiFi capable.

As for the CAX30 not handling the new speeds, I purchased that when I had the lower speed/tier plan, before the xfinity rep suggested upgrading speeds could possibly stabilize the connection ($2 more than my existing plan) and it is outside of the return window. I figure replace the cable first, see if that fixes/stabilizes the connection, and then replace the router.

Hi, thanks for the follow up. I'm waiting on the new coax to be delivered (scheduled for today) so that I can replace it. It's raining heavily at the moment so I might not be able to replace the coax until later or possibly even tomorrow.

There was another outage in my area last night and they worked on the pole behind my house. I ran another speed test (Ookla) after they did the work.  Prior to that latest repair work, the results were under 150Mbps, but after the repair it peaked a little over 600Mbps. There was another short disruption in service later last night (less than 30mins), and the current speeds today are between 300-350Mbps.

It looks like the repairs helped a little bit. The event log hasn't shown any criticals since yesterday, just notices. The last critical was a UCD invalid or unusable channel on 2/27/2026 at 21:28:59 which is around the time of the last disruption in service.

Downstream bonded channels are currently between 0.1 - 2.6dBmV & SNR is about the same. Four channels show correctables, most are low (<15), with the exception of one showing 162,683 correctables.

Power for the Upstream bonded channels are 42.0 - 43.3dBmV.

Downstream OFDM is 0.6 to -5.4dBmV

Upstream OFDMA had no changes.

I'll post full results once I've had a chance to replace the coax.

@kickflip425 Hello, you're welcome, and thank you for the update! I’m glad to hear that the work completed last night has helped improve your speeds. Once you’re able to make the changes on your end, feel free to share an update with us. We’d really appreciate it and will be here whenever you’re ready. 

Hi, here are the latest results. Also, within 10 minutes of connecting the modem/router to the new coax, I received a text from Xfinity saying there is a network performance issues that might be affecting my service that they need to repair right away. The event logs are showing criticals and notices. Ookla Speed Test is showing 185Mbps and 24ms Ping.

kickflip425 Thanks for retesting with the new coaxial connection. I'm sorry that we have an area issue being reported again. That will make it difficult to run a true test. I would like to investigate the area trouble for us as well since it seems to be reoccurring. Can you send us a direct message with your name and service address please? 

We can continue to work with our community here as well, but I would love to pull the levels from the devices on this side. 

Here are the detailed steps to direct message us:
Click "Sign In" if necessary
Click the "Direct Message” icon (upper right corner of this page)
Click the "New message" (pencil and paper) icon
Type "Xfinity Support" in the to line and select "Xfinity Support" from the drop-down list
Type your message in the text area near the bottom of the window
Press Enter to send your message

Hi, I did reach out by DM on March 3rd and the rep said there were more repairs in my area, they would follow up with me, and that "the reminder is already set on this conversation". My service is even worse, now under 51.74Mbps to my laptop and 17.72Mbps to my cell phone and I'm less than 30' away from the modem/router. There are no correctables/uncorrectables and there is nothing new in the event log. I followed up a few minutes ago to the DM and I awaiting their response.

@EG Thanks again for all of your help and I'm asking for a little more assistance. Do you happen to have any other tricks up your sleeve or know of anything else I can check on my end of things/equipment/settings/etc. that could be causing a problem from my end of things?