Resolved - From 10:08 PM Friday January 10th (UTC) to 1:21 AM Saturday January 11th (UTC), the bici proxy group was unavailable. This proxy group is a SOCKS proxy group in the EU Region.
Fixie uses AWS DocumentDB for some state. AWS made an unannounced change to the cname through which instances in the EU region connect to their managed DocumentDB cluster. This meant that proxy servers that had sufficient available, existing connections in their connection pool were able to serve requests without issue, but proxy servers could not start cleanly. (01:21 UTC — Jan 11)