I don't have a formal RCA from the facility yet but I do expect one sometime today or tomorrow.
The short version is essentially that there was a mis-ordered routing policy that resulted in unexpected withdrawal of the default networking route when a single carrier was removed from the transit mix.
It is normal from time to time for the mix to change - say a specific carrier/transit provider is experiencing packet loss or network issues - the network will be removed from the mix to ensure performance. In this case Hurricane Electric was being dropped from the transit due to issues with their network.
As this happened at the facility level it occurred on networking equipment we do not maintain nor have access to - unfortunately out of our control. We are confident that this issue will not recur.
If you have any questions about any of this please feel free to reply here or to open a support ticket.