Comcast XFINITY → [Connectivity] Slew of connection oddities - help, please

I have a wired connection: leased Arris WMB760a, Vonage adapter and desktop PC. My tier is Blast 50/10.

Saturday was connection issues day from hades. Mid-morning walked by desktop to see a Windows error message on the screen along the lines of "TCP settings incompatible with router". Don't have a router other than what's built-in the Vonage adapter. Speed test showed I was getting 49/17kbps !!! Another speed test had NO upload speed. Couldn't even get google or yahoo to load. Tried to use phone but fast busy.

Cleared cache/cookies, power cycled everything; restarted PC. Same error. Called Vonage. Fast busy due to poor connection. In the meantime, lots of T3 errors in log. Also noticed my downstream signals were varying from 0.xx to 4.xx.

Tried direction connection sans Vonage: no joy. Sometimes I'd get 50/4; othertimes, that lovely 17kbps for upload. Called Comcast and (luckily) got a rep who listened. During the call, the issues cleared up. An hour later, same thing but cleared up and (knock on wood) have cleared up.

Why would that TCP message pop up as I didn't dabble with anything and - while my cats are smart - they only chew the ethernet cables. Would it be anything to do with IPv6 of which I know diddly ?

Any ideas/help, please ?? Thanks very much in advance.

My log shows the CMTS MAC addy as CHANGING on 12/4/2014 ??? Log attached.

What are your upstream signal levels, especially when the problem occurs?

Upstream signals pretty much hang in there ranging from 41.25 to 44. They were 41.xx yesterday, I remember. Forgot to grab screenshots. (FWIW, my SNR has been hanging in there at 37.xx).

Here's what they are now. Thanks in advance for your help.
Downstream
DCID Freq Power SNR Modulation Octets Correcteds Uncorrectables
Downstream 1 101 681.00 MHz 0.23 dBmV 37.09 dB 256QAM 121044024 0 0
Downstream 2 102 687.00 MHz 0.47 dBmV 37.36 dB 256QAM 85177747 0 0
Downstream 3 103 693.00 MHz 0.43 dBmV 37.94 dB 256QAM 85064930 0 0
Downstream 4 104 699.00 MHz -0.06 dBmV 37.36 dB 256QAM 84288088 0 0
Reset FEC Counters
Upstream
UCID Freq Power Channel Type Symbol Rate Modulation
Upstream 1 3 22.60 MHz 41.25 dBmV DOCSIS2.0 (ATDMA) 2560 kSym/s 16QAM
Upstream 3 1 34.80 MHz 41.25 dBmV DOCSIS2.0 (ATDMA) 5120 kSym/s 64QAM
Upstream 4 2 27.90 MHz 41.25 dBmV DOCSIS2.0 (ATDMA) 5120 kSym/s 64QAM

nothing that has to do directly with your cable connnection will give a windows error.

you have a software issue on your PC.

also "alot of t3s", how many is alot?

did you recently install anything new on your PC? try a restore point, before you started having issues.

T3 - total of (errrm) 3 from Dec 4 - Dec 6. I think I meant to write "alot of errors". Sorry.

Haven't installed anything new. My ESET Security 8 does a lot of updating but I can't imagine it being the culprit. I run AV scans frequently and they come up nil. Haven't used a restore point since around 5 weeks ago.

Vonage swears they didn't put out new firmware. I know less than diddly about IPv6. Could that have anything to do with that TCP warning; or affecting that Vonage adapter.

Apologies if these are stupid questions, but don't have smart ones. THANKS !!