Sounds like something may be breaking down at a VLAN again. Saw this happen back in the spring of 2014. TWC caught it just on the other side of Cogent's exchange. Could be something funky going on with port/IP assignment for that one character or something. Each world service is hosted on multiple IP's, and your session is assigned a specific port ID as well. Just spit-balling...hard to say if it's plausible or not without looking at whether the assignments change when you switch characters though.

If you can pull in your ISP's Tier3 guys to look more closely at the specific route used for your characters, they may be able to narrow it down better so we can pass on relevant details to the proper party.