Hello,
not sure if this is a bug or not but it caused me and some others problems yesterday.
The transition on the old bridge that is in the 1st underdark area west of Sanctuary made the pc's walk about -through- the terrain & causes some sort of feedback loop [character walking back & forth endlessly not transitioning].
Relogging just stopped the looping/walking.
We managed to get across eventually, so that's why I'm not sure if it's a bug or not.