What about the time since that 3hour outage? Are you still getting any re-syncs?
I wonder, because that period continues to have some horrible drop rates, around 10%.
Each horizontal pixel is 100 seconds, and appears to be 100 pings. A 10% drop rate - if it were concentrated together within the 100s period, would be a 10second dropout - just long enough for a sync???
If it were following that pattern, then I guess you're getting a sync every 2 minutes. And that, IIRC, is the pattern seen by people with faulty modems (or faulty power supplies for their modems).