My internet goes out between ~9am and ~12pm every weekday

I seem to be having the same problem in the San Jose, CA area since January, and I nailed it down to the modem receiving very low downstream power and resulting low SNR from the modem log/status page, when the disconnection happens. For me, the problem seems to occur between 3 pm - 8 pm, when the power degradation occurs, and then after a while the downstream power (and SNR) goes back up to normal/good levels.

I reported it to Comcast, the first rep arrived at a time on a Friday when this transient problem wasn't there. So he poked around and left, without solving the problem that occured a little later the very same day. The next rep. came on a Sunday after I raised the unfixed issue with Comcast again, noting it wasn't fixed, its transient and so on. This rep. said there is work being done outside in Comcast's lines/network, which should fix the problem - and then poked around my apartment again. There was no problem inside my aparment - this setup (hardware, wiring, etc) has worked flawlessly for 3.5 years after all.

The fact that it is transient during some times during the day, and goes away by itself - coupled with my noted low downstream power at the modem when the line degradation happens - indicates the problem is fully with Comcast's network/hardware outside. However, I'm appalled that Comcast is clueless about what could be the root cause.

I'm looking to seek help from knowledgeable Comcast folks, rather than being given the run-around by the technicians who seem clueless. Anyone can help ?

More details on mine:

My neighbor is apparently running into the same problem (further suggesting that this is something external within the broader Comcast network).

He said that recently he has been seeing a couple hours a day when his internet and TV both get spotty, normally in the morning.

On 2/29, this went out and never came back.  A tech is coming out this coming Thursday, March 5.  My neighbor will try to let the tech know that there is a broader issue in the area and that it's often transient.  Fingers crossed.

He did say that Comcast ran some diagnostics from their side and thought they knew what the issue was.  

Any update? I've also been having very spotty internet since the beginning of the year... and I live in Texas! It's so frustrating!

Another update:

Talked with a second neighbor.  Her cable has been spotty for a month and she had a tech come out last Friday (Feb. 28).  

The tech believes he traced it to a pinched cable on a newly replaced electrical pole up the street.  PG&E replaced the pole a bit over a month ago, so the timing is fairly close.  

He told my neighbor that Comcast will have a crew out to look into it and hopefully fix it on March 5.  Fingers crossed this does the trick.

The behavior (going out at the same time each day) was likely related to heat expansion from direct sunlight in the morning hours, or at least that's the theory.

We'll see if the problem continues or if this resolves it.

Note how the timing of the failures follows sunlight/daylight.   Impedance increases with temperature.    Those of you seeing this sort of failure are likely to have your demarcation point be on the windward and/or sunny side of your residence.     If you have an old demarc exposed to elements and not inside a plastic-box-with-accressible-door, you can consider to request comcast to swap for the new/better demarc - the tech will cut off the old  corroded connectors & re-crimp new connectors & reconnect the cables and put it all inside the gray-or-green plastic box.        You can inspect the demarc yourself and provide photo of any evidence of corrosion or tell comcast if you find loose connections.   If the exterior cable-connections are anything less than 100% dry and are exposed to elements whatsoever, comcast going to swap it sooner or later as they are swapping them all across USA.   Call them and be nice and ask them to swap it sooner.     To be clear, comcast owns the demarc 100% and they will charge you z e r o to diagnose or swap it.    They only charge money if they have to deal with your inside wiring/network.     Also, consider to re-run your tests from the interior of your house as close to the exterior demarc as possible - with zero splitters - zero wifi - zero router - direct hardwire your computer to the cable modem temporarily in the basement if you are up for it.    This testing method eliminates your inside wiring from being part of the problem and tests only the comcast-owned equipment.   Pony up $10 to rent a comcast cable modem for the month to do the tests, if that helps to convince them.     They will refund it after you & the tech & more testing & a corroded demarc prove what the root cause was.  

While this could be the problem with temperature effects on Comcast's infrastructure, I can see no way to make the techs who come out to understand all of this you've stated. They are either ignorant or condescending/arrogant or both - when you can explain the transient nature of the problem. They also seem to be hyperfocused on pinning the problem on something "inside your home" (so that Comcast can charge for the tech visit, I presume). Speaking from experience on all of the above, with 2 tech visits.

That is the reason I posted here, hoping someone from comcast with knowledge and intelligence can help fix this.

Final update (hopefully):

Things have been stable again for the past week, so I assume whatever work they did out on the line did the trick.  

Very grateful to all my neighbors for pushign this as well, since I think it normally takes a number of reports before they'll start looking into that sort of thing.

Wow this sounds identicaly to the issues we have had for months and still continue to have.  At first Comcast determined it was the modem, then it eventually was elevated and determined it was massive interferance in the neighborhood lines. I talked to one tech after he climbed the poll and he found massive interferace and said he would fix it.  The issue kept happening.  Its less severe now, but still occurs 1-3 or more times a day.  More tech visits and more areas they find interferance on their polls.  Odd thing is they are showing the modem remains connected, when its been going down.  Now its suggested that one of my devices in my network is the probelm.  None of my neighbors have these issues as they are all on FIOS.  I finally ordered Fios for internet and for the moment I have both services. Fios (direct fiber into the house) has been down zero times in two weeks and Comcast continues with these periodic randome drops. Service was fine and mostly reliable except for reported area outages for almost two years and then a disaster for about the last six months.

Yoo @eviljosh im having the same exact issue!! Everything youve described is on point with my issue im even on the same modem arris sb8200 and recently tried using a netgear nighthawk modem and still having the same issue. Ive already had 2 techs come out but when they get here the internet is working.