One final post for the resolution to my problems before I let this thread go dormant.
The issue turned out to be an error with the modem itself but it wasn't damaged. The tech that came out said the issue was primarily with the modem using the incorrect software to boot. I interpreted this to be the bootcode as that is all I can see in the router's settings but I cannot confirm it as I did not screenshot that beforehand.
I had changed out two different modems in the span of only a month when I first replaced our Xfinity modem and I assume my first, much more weak, modem was still in Xfinity's system. I should have known this when I went to "https://www.xfinity.com/support/devices/#search" and had been told I was using an Arris SBG6700-AC instead of my SBG7400-AC2. The answer to the problem was right in front of my face.
The solution was fairly simple. The tech somehow marked that device as no longer being in use, re-authorized our cable and internet, and finally installed a noise filter on our internet coax cable. BruceW was correct with it being a hardware issue!
If you find yourself here and all of this sounds like the symptoms of your own internet connection troubles consider asking an agent over the phone if you have two modems activated on your account. If you do, ask to remove the older modem and ask for a complete re-authorization of your cable signal. Our WiFi is now up, stable, and super quick again.
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I have attempted a few live agent chats to see if our issues could be resolved without a technicians' visit but it seems as though not much could be done from Xfinity's end. In fact, as I type I am having another " DNS_PROBE_FINISHED_NXDOMAIN" error with oauth.xfinity.com and only that site for the moment.
A visit has been scheduled to see if they can find any physical issues with coax cables or other hardware. If any other users find their way here I suggest you do the same. Thank you @BruceW for all of your help and time.
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It seems as though I took too long gathering information. I restarted the modem again and used imgur instead.
Event Log: https://i.imgur.com/RJDA1oa.png
Device Status: https://i.imgur.com/jiuFhFU.png
Modem/Router Settings: https://i.imgur.com/l8pKHjP.png
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I really appreciate the help and apologize for not providing the correct information before. Here is all of the information requested in a few images. As well as those I have collected some information from my WAN, LAN, and wireless settings that might also help. Those settings were typed out in a text document but I have taken a snip of that to keep things as tidy as I can. I will be attempting to test an ethernet connection soon but I do not have a PC close enough to our modem at the moment. All coax cables I can access have been tightened but issues persist. A Comcast technician will need to be requested to check any other connections. Downstream Upstream Event Log Device Status WAN, LAN, and Wireless Settings
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We are currently having a very strange, somewhat frustrating issue on our Xfinity home WiFi network. All throughout the last few days (1-30-2020 to 2-1-2020) we will slowly lose the ability to connect to certain and seemingly unrelated websites. It will usually start with Google, which when connecting to it will give the error "DNS_PROBE_FINISHED_NXDOMAIN". Soon we won't be able to see YouTube thumbnails or comments. Then the videos won't even buffer. Eventually that gives a "No Internet" error. Sites like imgur and Reddit are available for a long time but cannot be loaded after enough time. Rebooting our Arris modem/router will fix this but only for a limited time. Four hours or so is all it takes to return to our "no internet" issues. We can live with this but, surely, rebooting our modem four or five times a day is not a true solution.
Before I get to attempted solutions let me list some information about our network.
*Performance Pro+ Internet Package (175 Mbps Downloads)
*Arris Surfboard SBG7400AC2 (router & modem)
* DHCP enabled for both IPV4 and IPV6
* 2.4 GHz & 5 GHz enabled
* DNS Override Enabled (Primary: 220.127.116.11, Secondary: 18.104.22.168, Tertiary: 22.214.171.124|Similar IPs for IPV6)
All but one device, a Windows PC, use Chrome for their web browser. Android Phones and Windows PCs alike encounter the same issues. Both Firefox and Chrome have the exact same results.
Three PCs use the Origin, Steam, and Uplay web clients for games. Every client will eventually report that they are offline and cannot download games or display web pages.
So far I have rebooted the gateway through both the built-in user interface and the Xfinity website. I have disabled DNS override, changed the DNS IPs to be Google's 126.96.36.199/188.8.131.52, and manually changed them to Xfinity's own 184.108.40.206 / 220.127.116.11. And finally, with few ideas left, I tried pulling the power plug and waiting five minutes in the hopes that the device just needed a moment to cool down and a hard reboot.
DNS changes have no effect. Reboots all have the same result. We are able to access all websites without any issues for a few hours before we slowly, one by one, lose access to certain websites. It is very strange to lose Google while researching the issue but still being able to use DuckDuckGo to continue the research. As I type I have lost access to even that yet am able to use any Xfinity sites. I'll be contacting Xfinity support Monday but I was hoping to get these issues fixed before then.
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