After clearing the ground floor of the Lighthouse Ruin in Ondra's Gift, I found the door leading to the starcase to the next floor appeared to be open but was impassable. Activating the door produces the opening sound, though it does not animate; this renders the door passable.

 

As I left the area to rest and only discovered this on returning, I do not have a save directly before this bug occured.

 

https://www.dropbox.com/s/i7k5q3bthbbvjv3/lighthouse_door.zip?dl=0

I ran into the same bug and worked around it the same way. The impassible part is just the strip of floor that is covered by the closed door.