Constant Internet Speed Reduction after 9PM Every Night

Well in my 17 years of helping here I can say that I have never seen downstream power levels look quite like yours do ! They are all over the place...... The SNR's are mostly too low as well. There is a bit of reverse cable tilt going on as well.

There is a serious connection quality problem somewhere. You are asking for help here on this forum but this is going to *take boots on the ground* to fix ! Feel free to show this thread to the techs when they come on Thursday. And let them know everything that has been done so far !

I'll add this.

Bear in mind that if the premises facing techs can not find or fix a problem at your home, it is they who are responsible for escalating it to their line / network / maintenance dept. techs. The problem may lie beyond your home in the local neighborhood infrastructure somewhere but it is their S.O.P. to start at the home. Make sure that they write up a trouble ticket for / refer this to the maintenance dept.

Good luck with it ! Please post back with how things turn out.

EDIT: Not sure why my replies were private, but going to repost my messages as comments this morning.

Thanks for the input.  I do have a trouble ticket ongoing, and was explicitly told the techs would be checking the neighborhood.  I've had good/bad experiences with xfinity techs though, some that explain everything to me and make an effort to change things, and others that show up for 10 minutes and leave without speaking to me.  Hopefully the tech will be a good one this time.

Yeah I also agree the power levels are extremely odd, and don't seem to be consistent at different times of the day.  I'm gonna post another screenshot below for 8am on 4/14/2021 when my speeds are currently the worst.  I expect the issues to go away around 9am like they always do, so I'm also going to add another screenshot then, so I have it all documented in this thread.

Quick question for any experts on this forum as well.  Do you know of anything that would cause issues only after sundown in the network infrastructure? Its really odd all my issues start 30 minutes after sunset, and fix themselves 30 minutes after sunrise.   I figured it was probably network congestion since it was happening in the evening, but I can't imagine my signal becoming this bad because of congestion.  It almost seems like its a malfunctioning piece of hardware somewhere that is throttling down at night.

Looks like I'm getting constant disconnects now at 2:30pm, while trying to work.  Posting another modem status for reference.  Lots of Uncorrectables again.

Don't want this to sound like a snide or sarcastic comment but at night people are more prone to use more services and soak up the bandwidth.  Therefore its more likely that your service drops at night especially if you live in apartment \ town home complex.  Cable is shared with hundreds  of people around you.. so it's not a dedicated connection.  Just FYI.  I being sincere and not trying to give you grief.

I do think the problem is the modem.  Get the XB7 gateway.  If you are still using modem and router combo that's the old way.  The better and more advanced option is gateway which has the modem \ router in one unit.  Arris is good but I think yours is defective.. maybe even out of date, it's better to trade up.

Just take it to comcast store and ask them to swap it for a gateway (XB6 or XB7 they are similar but XB7 is the newer on and it might depend on service level if you can get it.).  I have relatives that had the same problem which is how I know or suspect the problem. But again don't want to come off sounding like you are the problem just saying that you could get better service with a gateway.

Good luck!

@atl_vm  FWIW. The OP's signals are horrible. A new / different device won't fix a line / connection quality problem..

@atl_vm Thanks for the comment. I do understand the connection is shared, and that network congestion can happen at night.  However I will not accept the speeds dropping to 5-10mbps at times when I pay for 200mbps.  If it was just dropping to 80 or even 50mbps during heavy load I wouldn't complain.   I'm also not willing to rent more equipment from xfinity and give them more money, when I can have my own cable modem.  I have 3 on hand I've tested this issue with and the issues always come back (arris surfboard, a netgear CM400, and another motorola DOCSIS 3.0 modem).  I will say the issues do get better for a bit after activating a new modem, but eventually within a day or 2 the signal becomes horrible (Unlocked Channels, lots of uncorrectables, and varying power levels).

As @EG stated this seems to clearly be a line/connection issue, and I'm leaning toward some kind of node/hardware malfunction because it happens regularly on a schedule.  Though I've been getting disconnects and modem resets now in the afternoon.

Luckily, my local power company is installing fiber near-by, and should have lines buried in my neighborhood later in the year, at which time I'll be kicking Comcast from my life.   However if the issue isn't fixed soon, I'm contemplating signing up with a Fixed Wireless company, that some of my neighbors use that provides download speeds of around 80mbps, and much better upload speeds than Comcast.  At least in the interim until I can get direct fiber.

Lets hope they can fix the issue though.