Intermittent Internet Outages Stopped by Disabling IPV6

I fixed my intermittent Internet outage, having struggled to find a solution online that matched my symptoms, and wanting to share my solution in case it helps others.

We have Internet, U-Verse TV and home phone (VoIP) service.   We were using a Pace 5268AC gateway only (no IP passthrough to another router).  We don't use the Internet heavily (no streaming/gaming, just watching U-Verse TV and light Internet browsing from 2 home computers).

We were experiencing random outages of all 3 ATT services multiple times per day, day or night, regardless of whether any devices were being used.  The outages affected all wired and wireless devices using the gateway.  On our Pace 5268AC, the Service and Phone 1 lights would go out and take 2-3 minutes per outage to come back to solid green.  The System log in the gateway indicated that the DSL link had been lost each time we observed the loss of services.

One ATT agent sent us a new Pace 5268AC, which didn't solve the problem - same random losses of DSL service in the System log and outage of all our ATT services.

Another ATT agent observed 'something' in the gateway and dispatched a Tech to our home, who replaced the Pace 5268AC with an Arris BGW210.  But the problems continued, and the log file (such as it is in the BGW210) was only indicating 'Other DoS Attack' about the time we were observing the random service outages, still multiple times per day, now lasting 1-2 minutes each time.

I noted that the 'Other DoS attack' log messages were coming from seemingly random external IP addresses, and that all of those IP addresses were IPV6.  I finally found mention in one problem report about disabling IPV6, and tried it.

I disabled IPV6 in our BGW210 and the outages went away completely, from 4-5 times per day to zero in the past 7 days.  So far, there have been no side effects from the action, and I recognize that I'll probably one day need to re-enable IPV6, but for now am enjoying the lack of outages.