intermittent desyncs and disconnects getting worse

Additional logging from overnight:

This may or may not be the root cause of the problem (YMMV) but it should be addressed regardless.

The downstream power is high / strong. It may be over-driving the front-end receiver circuit of the modem. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels.

Is there a drop amplifier on the coax cable line leading to the modem ? If so, try removing / bypassing it and see. If not, you can try installing a -6 dB forward path-only attenuator pad such as this one on the coax port on the rear of the modem to knock that power level down and see;

https://www.amazon.com/FPA6-54-Forward-Attenuator-DOCSIS-Internet/dp/B08KTRC3XZ  

It won't affect the upstream power level which is within spec. Good luck !

You're welcome ! Please do post back here with how it goes, thanks.

@user_71gucl 

Thanks for the update. Fingers crossed ! 🤞

About a month ago I report a similar issue here; thanks to forum user EG I found what I thought was the work-around (attenuator for downstream power), but in the last couple of days the problems have returned and are at least as bad (if not worse) than previously.

Original forum post for reference: https://forums.xfinity.com/conversations/your-home-network/intermittent-desyncs-and-disconnects-getting-worse/6530a1f0e05b5f65da02f615

Here are event logs (Motorola MB8600) from the last 24hrs, excluding "Notice" log level events:

Downstream channel status:

Upstream channel status:

Fingers crossed one of you wizards has another miracle in store...

Just to rule out at least one possibility, I got a newer cable modem yesterday (Arris S33), but it quite clearly has not helped.

Updated Connection status and Logs from the last ~hour or so below...

This is starting to feel like a personal blog...

I took a look at the Comcast installed box on the side of my house, and while everything looks ok there, I did find an unnecessary splitter; I've removed it, hoping it might help the signal strength (if that's even the issue at this point), but it unfortunately hasn't seemed to help at all.

More event logs from this afternoon:

For anyone still following along at home, Justin kindly took a look at what he could remotely, and determined that my own signals as well as some neighbors in the area "don't look solid", so we agreed to have a technician come out to have a look. That should happen mid-day on this Tuesday the 5th, after which I'll follow-up here with what we've learned.

Thanks for your time and help today, Justin!

tl/dr:  things are better

Last night and again this morning I received a call from Comcast Tech Support; apparently my issue had been escalated to their team. Both people I spoke with indicated "something" had been investigated and corrected, and asked if my service was now working properly. I tried to explain to both that my issue was intermittent; and, while on the phone with them things were normal, I didn't necessarily have any expectation that things would continue to be normal given the recent history. I do not wish to speak unkindly to those who were tasked with these follow-up calls, but I got the feeling they were primarily interested in cancelling the in-person tech appointment, which we ultimately agreed to do.  Assuming the issue actually has been corrected by someone/something, then they obviously were calling for the right reason.

In both cases I asked for an explanation of what had been done, and in neither did I get much of an answer; this morning's call the support person simply said that some "signal" had been sent and that now everything looked good...    I did attempt to explain that initial investigation by Justin indicated that my issue was apparent not just for me specifically but also in neighboring homes as well, which to me spoke to wider issue. Nevertheless, I couldn't seem to get any further information, though perhaps the person I was speaking with simply didn't have details on precisely what was done. I'm mentioning all of this solely for the future person who searches for resolution to a similar problem, and I'm sorry you won't find much here beyond "be persistent with your need for help and hope support is able to find 'something' to correct".

Nevertheless, things have been stable for at least the last 24hrs, so that's a step in the right direction. Thanks again to Justin for initiating, investigating, and escalating.

Well, the joke's on me (again).

Beginning again this morning are more T3 timeouts, Dynamic Range Window violations, Unicast Maintenance Ranging, etc.

Can't believe I let myself be talked into cancelling the on-site tech appointment, which would have conveniently been this morning.
Hopefully I can have one rescheduled relatively quickly.
More to come...

On-site tech was here today.

He found a loose connection at the pole near my house, and replaced it; he explained this can happen naturally over time depending on climate, weather conditions, etc.

He additionally noticed the connection to the box on the outside of my house (the coax from the pole to the house) was slightly degraded as well, and went ahead and replaced this connection; similarly to the above, this apparently can be a natural phenomenon over time and he didn't seem particularly surprised by it.

Unfortunately, within a half hour of him leaving, my modem is once again logging some t3 time out events and unicast maintenance ranging errors. I have not yet personally experienced the same loss-of-connectivity issues I've been having, but I assume the logging is not a good sign and it's only a matter of time...

Will keep monitoring and escalate again if today's visit hasn't found the true source of the errors.

On-site tech #2 was here this afternoon (an hour early, bonus points for him!).
He was not aware another tech had already been to look into this issue, so I went through all of the history I could recall as well as what I understood had been done the day before.

He put some monitoring equipment on the inside line to the cable modem, and then again outside at the box on the side of my house, and saw nothing wrong with any of the signals/power/noise/etc.

He could think of no other reason I would be experiencing the issues I've been seeing, except for the possibility that the cable modem was overheating, so moved it to a location with better ventilation. I did explain that this was a new modem, that I had replaced it in the last week or two, and that even with the prior modem I had experienced the same set of problems/errors.

In any event, as things were "normal" while he was here, he was out of options.

In the hour or so after he left, I captured these from the modem's event logs:

Connectivity has been normal for the hour following the last logged event above, and I expect it to be fine until whatever gremlin is causing the periodic issues wakes up and wreaks some more havoc.

I've since been in touch with support once again, and they've arranged for another on-site tech visit for this coming Tuesday morning, so I will once again follow-up here afterwards.

I was off by one day, the follow-up on-site appointment was today (Monday).

Today's visit was the best by far, by a Comcast employee (as opposed to the consultants that are often used); he immediately acknowledged there were myriad signal problems in the area, and never even bothered coming in my house. He had also arranged ahead of time for a partner employee with a bucket truck to arrive with him! As at least an initial step, they reran a new coax line from the top of the pole near my house to the xfinity box on the side the house, and had me reattach a signal attenuator to the cable modem (the first on-site tech removed mine......and he kept it). Signal levels once again look good, and I will continue to monitor over the next few days.

The tech stated that while this should definitely help my recent issues, it will not necessarily completely solve them, as the signal issues in the area could still cause widespread/periodic problems; ultimately they made need to continue to do similar work as they did for me today at other residences/businesses in the area (that is, if I or enough other people keep escalating issues).

Will try to report back here in a few days with an update.

BIG thanks to today's techs, Wes and DJ.

Things have been significantly better, almost perfect.
I've had a single error (a t3 time-out) since the techs were here on Monday, so an enormous improvement overall.

I'll obviously continue to monitor, and will re-escalate if/when things become problematic again, but for the time being things are "good".

Thanks again to all the support personnel (both online and in person) who have helped!