I have seen that quite a lot in Auridon, it usually happens when a lot of people are in that zone doing Dolmens or whatever.
Happens now and then in Cyrodiil to.
I get that sometimes too. My only guess is that the zone hasn't loaded properly. If I zone in and zone out, it's usually gone. Merely moving around the zone doesn't help, however. Daggerfall's especially bad for it.
It's a texture bug that happens randomly. Restarting your game fixes it. Maybe even a /reloadui will do it (I can't remember as I haven't had it happen in a while).
it is a texture bug. It usually happens when there are a lot of people in zone, or if you are wayshrining a lot in the same zone. Usually rezoning or relogging fixes it.