UPDATE 17:38 -0800: HE.net says they are still investigating. The other BGP peers for 55 S. Market have similar uptimes to ours so evidence points to something at 55 S. Market.
We had a network outage of 6 minutes from about 12:12 to 12:18 PST -0800. The symptoms were quite similar to before. I will post more details as they become available.