This happens often in various places. Something in the game since pub95 is buggy with doors. The doors in Blackthorn by the captains hallway, Doom, player housing(rarely), and various other places(anywhere with doors) disappear for me regularly. I believe it has something to do with unloading and loading the tile over and over, but I cannot verify because I have not been able to manually recreate the bug, it just happens.
Shard: Legends & rarely Siege.
EDIT:
Reporting to
[email protected] with a link to this thread for your picture, I never thought to actually screen shot when doors disappeared, I just thought of it as an advantage because I no longer have to hit my open door macro