No Ranging Response received - T3 time-out every 2 hours

... T3 time-out every 2 hours ...

All of the upstream power levels posted are out of spec (too high), suggesting that there is most likely a poor connection between your modem and Comcast's network. Problems like this are often due to corroded coax connectors or damaged coax cable, usually in or near your home. Running the cable through a surge protector, a defective splitter, or too many splitters can cause signal problems as well. If there is an amplifier in the line make sure it's getting power. 

If you want to troubleshoot this yourself, please see Internet Troubleshooting Tips.

If you can't find the problem or you'd rather have Comcast take care of it and an employee does not respond to your message here, call them at the phone number on your bill or 1-800-Comcast, or use one of the options on https://www.xfinity.com/support/contact-us/. It's not likely they can fix the problem remotely. If not, insist they send a tech out to identify the cause and correct it.

If the tech finds bad coax, splitters, amplifiers, or connections in your home (even if Comcast originally supplied them) you'll probably have to pay for the visit ($70-$100) unless you have their Service Protection Plan ( https://www.xfinity.com/support/articles/service-protection-plan, closed to customers that don't already have it). If the trouble is due to a faulty Comcast rental device or anything outside your home you shouldn't be charged.

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However even with this change, still I see the same behavior - disconnect after 2 hours:

... This seems to have improved the upstream power levels a bit ...

They're better, but now borderline. It's best to have them in the middle of the Internet Troubleshooting Tips range, which would be +40 to +45 dBmV. Also what do the downstream channels look like now? They should be 3 or 4 dB higher than they were with perhaps slightly better (higher) SNR, but it's always best to check after making any changes to the coax line.

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

You are pretty much spot on - downstream power increased, SNR looks to have stayed mostly the same.

Still T3 every 2 hours (for some reason the modem clock is 1 hour behind):

Time Priority Description
2023-6-6, 16:03:31 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=[REDACTED];CMTS-MAC=[REDACTED];CM-QOS=1.1;CM-VER=3.0;
2023-6-6, 16:03:31 Warning (5) MDD message timeout;CM-MAC=[REDACTED];CMTS-MAC=[REDACTED];CM-QOS=1.1;CM-VER=3.0;
2023-6-6, 14:00:07 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=[REDACTED];CMTS-MAC=[REDACTED];CM-QOS=1.1;CM-VER=3.0;
2023-6-6, 14:00:07 Warning (5) MDD message timeout;CM-MAC=[REDACTED];CMTS-MAC=[REDACTED];CM-QOS=1.1;CM-VER=3.0;
2023-6-6, 11:56:01 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=[REDACTED];CMTS-MAC=[REDACTED];CM-QOS=1.1;CM-VER=3.0;
2023-6-6, 11:56:01 Warning (5) MDD message timeout;CM-MAC=[REDACTED];CMTS-MAC=[REDACTED];CM-QOS=1.1;CM-VER=3.0;

@Xfinity Support   can you please provide guidance for next steps to get this resolved please. 

@jmsoz @XfinityStephanieK 

Please circle back here and post any possible solutions for the issue here in these open forums so that all readers here may benefit from the exchange / info. This is in keeping with the spirit for which these public help forums were originally intended. Thank you.

Having the same issue since at least fall of 2022. I was running a straight line from the service pole to my modem, no splitters. Had a tech out and they described a known issue with upstream noise somewhere in the area, which crews hadn't been able to locate. They suggested buying a newer modem, with more upstream channels, so it had more options to switch to when one went down. My modem at that time had 4, so I upgraded to one with 8. Turns out, they only use 5 to begin with. They also said my signal was calibrated for the home to have a splitter, and since I didn't, adding one would adjust my signal levels back into ranges where it wouldn't exceed the limits and drop the channels as often when the issue would occur. They installed a splitter with terminator caps on the unused positions, and replaced the lines from the service pole to my home as well. The only other object in line between their service and my modem is a MoCa filter and all cables from the exterior junction box to the modem were installed fresh by the installation tech not quite 4 years ago, with zero damage or manipulation in between.

With the new modem, a Netgear CM1000v2.   I did notice improvement, but still intermittent issues. It's common around lunchtime/early afternoon, but does sometimes happen later in the day as well. The upstream light will start flashing, I lose my connection to my work VPN, causing some hazardous situations for me, professionally. Recently, it has gotten worse, similar to last fall in frequency. 

I had a tech out again last week on an unrelated matter, same one actually, and had them check the noise levels, but being the wrong time of the day, they were not able to observe the issue.  I've since performed a complete overhaul of my entire network, being more on top of monitoring this issue, and what I learned here, I see now that my upstream dB are also on the upper end of the range, between 45.5 and 48.5dB. I expect that when the issue arises, those may be spiking too high, and dropping channels, but I haven't been able to directly observe this on the modem yet. 

I'm seeing all kinds of T3 and T4 errors on the logs, in a 16 hour period today, there were 40 instances of warnings, either:

Warning (5) Dynamic Range Window violation,

or

Warning (5) RNG-RSP CCAP Commanded Power in Excess of 6 dB Below the Value Corresponding to the Top of the DRW;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;

and 

Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;

Yesterday, when I gathered the logs from the modem, there were about 55 Entries in total, going back just over a month in range, so it seems to be happening more frequently now. Interestingly, there are numerous instances in that collection with "Time Not Established". Again, almost all of those are Critical (3), with much less Warning (5). In that collection, there's more variety, with repetitive cycles of the following type errors, with various orders each time: 

Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;

Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=[redacted];CMTS-MAC=[redacted but was all zeros];CM-QOS=1.1;CM-VER=3.1;

No Ranging Response received - T3 time-out;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;

REG-RSP-MP Mismatch Between Calculated Value for P1.6hi Compared to CCAP Provided Value;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;

RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;

Dynamic Range Window violation

SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=[redacted];CMTS-MAC=[redacted but was all zeros];CM-QOS=1.1;CM-VER=3.1;

Resetting the cable modem due to docsDevResetNow

TCS Partial Service;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;

The tech lead me to believe there would be an entire system upgrade happening in my area sometime in the next few months, which also implied the motivation to solve the issue in the area was probably low, since a lot of the equipment would be replaced, but this will cause issues for me professionally if I have to wait that long. 

Since the upstream signals seem to be high in general, but the logs show both exceeding top values of dynamic range, and commanded power in excess of 6dB below the top, what's going on here?

I'd gladly provide the full logs to any xfinity representatives for review. I just need this solved. I'll install anything needed to help smooth it out further, or bring things back to the middle ranges if needed. 

An overall attenuator or a splitter would increase the upstream power. It works the opposite way for the downstream power. It decreases it.

The object would be to decrease the attenuation of the line thereby decreasing the upstream power. This is done by improving the line / hardware / connection quality. Removing any impairments.