Sync and connection issues after upgrading to XB8

Edit: I switched back to SBG6580 and will be returning the XB8. This has been the most frustrating experience I've had with any company.

My recent experience with Comcast has been extremely frustrating. Even as I was typing up this post, the forum gave me a popup telling me that "your session has expired" with the only button being Refresh. There was no way to dismiss the popup, and clicking Refresh wiped out everything I had typed up. This is not acceptable.

Last month I decided to upgrade from my own SBG6580 to a rented modem. Other than an occasional dropped packet I have not had any connectivity issues with SBG6580 and I've been using it for over a decade. But it's a 14 year old piece of equipment and I wanted to upgrade for several reasons, like it being unable to sustain high speeds (overheating, I suspect), having upload capped at 5 mbps, and old WPA2 wifi encryption.

Activating the XB8 from the app did not work. Activating it through the phone did not work. "Advanced" support had me reboot it with a button on the back. That did not work either.

Tech came out and spent two and a half hours trying to get it to work. He replaced a lot of the coax outside the building that leads to the "box", the coax between the splitters, replaced the end of the cable inside, and a different XB8. He could not get it to work. He said the problem was that a single tap leading to the building was being split 16 ways. So I went back to my SBG6580, which was re-enabled, got provisioned and was up and running in less than five minutes. 

Another tech came out and he got the XB8 to work right away. No idea what was different this time.

It's been working at gigabit speeds for two weeks. Until today when I had to unplug the power to plug it in elsewhere, which rebooted the modem. It would not sync afterwards. It kept getting stuck at flashing green light, and then going to solid red after about ten minutes.

A few times I did get an internet connection but it was so slow that it was unusable. A webpage would take a minute to load with massive packet loss. I think the light was blinking white during this time.

Eventually I called Comcast and after a reboot from their end it started working. Not sure if it was just luck or they did something different from their end than merely restarting the modem. All in all it took me two hours and a dozen reboots to finally get my internet connection back after merely restarting the modem.

However, now the connection is unstable. Every 10-15 minutes the connection drops for about thirty seconds to a minute, or even longer. Here is what "ping 75.75.75.75 -t" looks like when the connection drops:

Reply from 75.75.75.75: bytes=32 time=13ms TTL=55
Reply from 75.75.75.75: bytes=32 time=12ms TTL=55
Reply from 75.75.75.75: bytes=32 time=12ms TTL=55
Reply from 75.75.75.75: bytes=32 time=12ms TTL=55
Reply from 75.75.75.75: bytes=32 time=15ms TTL=55
Reply from 75.75.75.75: bytes=32 time=14ms TTL=55
Reply from 75.75.75.75: bytes=32 time=11ms TTL=55
Reply from 75.75.75.75: bytes=32 time=13ms TTL=55
Reply from 75.75.75.75: bytes=32 time=12ms TTL=55
Reply from 75.75.75.75: bytes=32 time=12ms TTL=55
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Reply from [redacted]: Destination host unreachable.
Reply from [redacted]: Destination host unreachable.
Reply from [redacted]: Destination host unreachable.
Reply from [redacted]: Destination host unreachable.
Reply from [redacted]: Destination host unreachable.
Reply from [redacted]: Destination host unreachable.
Reply from 75.75.75.75: bytes=32 time=1106ms TTL=55
Reply from 75.75.75.75: bytes=32 time=12ms TTL=55
Reply from 75.75.75.75: bytes=32 time=12ms TTL=55
Reply from 75.75.75.75: bytes=32 time=14ms TTL=55
Reply from 75.75.75.75: bytes=32 time=12ms TTL=55
Reply from 75.75.75.75: bytes=32 time=11ms TTL=55
Reply from 75.75.75.75: bytes=32 time=13ms TTL=55
Reply from 75.75.75.75: bytes=32 time=13ms TTL=55
Reply from 75.75.75.75: bytes=32 time=12ms TTL=55
Reply from 75.75.75.75: bytes=32 time=13ms TTL=55
Reply from 75.75.75.75: bytes=32 time=13ms TTL=55
Reply from 75.75.75.75: bytes=32 time=13ms TTL=55
Reply from 75.75.75.75: bytes=32 time=13ms TTL=55
Reply from 75.75.75.75: bytes=32 time=13ms TTL=55
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Reply from 75.75.75.75: bytes=32 time=14ms TTL=55
Reply from 75.75.75.75: bytes=32 time=14ms TTL=55
Reply from 75.75.75.75: bytes=32 time=26ms TTL=55
Reply from 75.75.75.75: bytes=32 time=16ms TTL=55
Reply from 75.75.75.75: bytes=32 time=11ms TTL=55
Reply from 75.75.75.75: bytes=32 time=13ms TTL=55
Reply from 75.75.75.75: bytes=32 time=14ms TTL=55
Reply from 75.75.75.75: bytes=32 time=11ms TTL=55
Reply from 75.75.75.75: bytes=32 time=12ms TTL=55
Reply from 75.75.75.75: bytes=32 time=13ms TTL=55
Reply from 75.75.75.75: bytes=32 time=13ms TTL=55

This is over ethernet and affects multiple devices when it happens, connected to different ports on the XB8. During this time the modem light remains at solid white.

I never had this issue on my SBG6580. 

At this point I feel like calling Comcast support is pointless as they work off of a very small script and have no ability to troubleshoot what is going wrong, and the call will end with them sending out another tech (and I might get charged $100 for "professional installation" because I have a "new equipment" code on my account--or so they told me). The techs that come out don't have much of a clue either. If the modem fails to sync they have no idea why.

Now I'm afraid to even restart the modem for fear of not getting it to sync again. And if my modem ever reboots by itself, or power goes out, or I need to restart it for whatever reason, I might be in for another multi-hour session of trying to get it to sync.

When the connection is working the speeds are fine. Doing a speed test off of the 2.5 gigabit port gave me almost 1200 mbps down and 62 mbps up.

Where do I go from here? I'd buy my own modem if I thought it would solve the issue, but what if it has the same problem as the XB8? In that case I feel like I'd get even less help from Comcast than I am getting now.

I can always go back to SBG6580 but that would be a last resort. 

What is causing these issues?

Why does SBG6580 work fine while XB8 doesn't?

Is the 16x split from a single tap the problem (It's a 2x splitter into two 8x splitters)? If so, how do I get Comcast to do anything about it?

Would going to a slower speed tier help?

Would it help to reprovision the modem to get a different set of frequencies?

Edit: Here is downstream connection stats from the XB8:

Here are the error counts:

It says Channel 20 is the primary channel, and that's the one getting a lot of errors.

And Upstream stats just for completeness:

Edit #2: The 30-60 sec connection drops are getting worse. Had one last 15 minutes where a ping would only sporadically go through.

Edit #3: Called support. They said they'll send a tech out--no charge because the modem is already activated. Then when they went to create the ticket they said it will be $100, contradicting what they said earlier. So, that's not an option.