Download speed drops to ~30mbps on a 500mbps plan daily. Upload speed unaffected.

Download speed bottle-necking around 30-35Mbps is usually a sign the modem is entering "partial service" mode. This is caused by a problem with the signal going over the coax for service. Do you have Panoramic gateway? Also, how does the coax get from the street/pole to the room the modem is in? Any splitters, amp, filters? Last, when did the problem start and did anything change happen around then?

PS. I assume this is affecting both wired and wireless connections.

I'm having this exact same issue, starting yesterday. Here are the signal levels from my modem.

Located in Phoenix, Arizona and I pay for 1gbps, started dropping to 32mbps yesterday randomly. I have a 4 year old Arris S33 modem so I don't mind trying a new one, but others have said new modems don't fix the problem.

I get my full speeds through the router, it seems when I'm saturating my network in full when downloading a game on steam is when it causes the drop (started happening yesterday)

When it happens again I'll do a speedtest direct through the S33 and get the logs without the MAC address.

 I don't change the ethernet at all. Like I said everything's been working perfectly fine until yesterday.

This is what is happening for us... Is anyone else experiencing this same issue and frustration??

Our speeds are regularly less than 10mbps and they want to charge us for their tech to come out, but cannot articulate what their techs would be able to do for us. When we restart the modem, our speeds pick back up to about 300mbps, and then after about 20 minutes our internet slows back down to unusable speeds. I can tell this gets worse towards the end of the month as we use through data, but I pay the additional $20 for unlimited data, so what am I really paying for when I am stuck with dismal internet speeds? I am paying $170/month total for this and gigablast, and the only thing their support does is push their equipment for an additional monthly fee, along with another $10/month for their service calls. I understand the service fee to some degree, but since this is an issue with Cox throttling the internet, I would almost knowingly be wasting my money. I know not to expect 1 gig of internet speed, but for what I am receiving, shouldn't I be paying for the lowest internet plan, and not $170/month? Also, this seems to have gotten worse since 2Gig is now available.

I have the recommended Docsis 3.1 modem, and am getting these slow speeds even when I am directly connected to the internet (not on wifi).

Same thing happening here! I can't believe we are paying $150/month for this! 

I signed up just to put my voice into this.

I've been experiencing the same problem for about 2 weeks as well. 
I have a Netgear Nighthawk CM2000, and my downstream is only locking one of the 2 channels. 

Initially I was having dropped packets (Ping timeouts) about 5 or 6 consecutive pings dropped per hour, which were bad enough to know me off a Teams/Zoom meeting. A tech came over, and saw nothing on their pings. He did replace all the Coax terminations on all endpoints, and they even ran ping-plotter to my neighborhood, and didn't see anything. So they, of course, blamed it on my modem, being faulty, etc... 

Of course, on my end, I can't update firmware or do anything on it as firmware is pushed from their side. Magically, my ping drops stopped occurring. (That mostly proves that my modem was not at fault, but something on their side that got addressed)

Fast-forward about one week, my download speed degraded down to about 28-30 Mbps (I am on a 2.5Gbps / 100Mbps) connection. 

I opened a ticket with support, and they started giving me a bunch of ridiculous suggestions to fix this, like "Update your OS", and "your Antivirus may be out of date". (I kid you not, I have the chat)

I should mention, the tests I did were disconnected from my Orbi Mesh network, and connected directly to my laptop via an Ethernet cable, and receiving a public IP directly on my laptop. (So NATing) 

After a modem reboot, I can do about 2 or 3 speed tests at 2.2Gbps download speed, and then a few minutes later, it immediately drops back down to 28-30Mbps. (sometimes even down to the teens)

I am willing to admit that my modem could be the culprit at this point, but it is literally the last "device" between me and Cox, and I am willing to buy another one and try it out, to rule out the modem being the problem, even though I am not convinced that it is, given that the issue with the ping request timeouts resolved itself without me touching the modem. But if I need to escalate the issue, I want to be able to say that I've literally replaced every piece of equipment on my end. 

I just really really don't want to have to replace the modem with their Panoramic Modem/Router/WiFi , because I have additional devices on my network that I need to be connected, and also want to be able to use my Orbi system. 

Does anyone have any recommendations on modems that work better than the CM2000? I would appreciate any insight anyone might have regarding this. I am at a loss, and I have no better alternatives for internet in my area. Hate being held hostage by a monopoly! 

p.s: I don't know about you, but the rep I was chatting with refused to give me a ticket reference number, but instead gave me a phone number to call, to start the process all over again. He also refused to have a manager call me after I requested it. They also don't allow you to save your chat transcript after a chat. This should tell you something about accountability and obfuscation of their communications to disarm the customer from building a case. What a joke of a company.

Hi, 

I apologize that you have had this experience. This does sound like a localized issue.  Have you tried connecting the modem to a different power outlet and plugging it directly into the outlet if you are using a power strip? Sometimes, a fluctuation in power can cause intermittent connection issues or slow speeds.

We will be glad to investigate this further with you, Please contact us privately with your account information. Our email address is cox.help@cox.com. Please be sure to include your name, full street address, and a link to your forum post. As for which device to go with I'm not able to recommend any specific 3rd party modem, but we do have a list of all modems that are verified compatible with our network listed at https://www.cox.com/residential/support/cox-certified-cable-modems.html

Greg