Finally looking in to the issue, it seems that us9 and us10 were only impacted briefly this morning. us9 received a small spike at around 8:00 AM and a larger one 10:30 AM, while us10 got a spike at around 10:45 AM about four times as large.
us6 has been flagged for sending a very large amount of traffic and I'm working with support to get more information. No clear indicators in the server logs. I will be attempting to transfer us6 to a new node, but I have limited network access at the moment as the server has been quarantined.