It seems to be a well-known bug which happens when a player groups up in Cyrodiil.
I personally don't have this bug, but i have noticed that i start lagging immensely for about 30 seconds whenever i group up in Cyrodill. Which is pretty odd considering the rest of the game runs as smooth as butter.
Currently playing:
Swims-In-Sap - CP200+ - Argonian Templar
I like my healing like i like my characters: generic