A friend and I completed “Halls of Atonement +10” twice – most recently yesterday (of course intime). Unfortunately, the “Dungeon Port” achievement and the dungeon port itself has not been unlocked. The Game Master recommended that I report the bug.
I also read on the US forum that several people are having the same problem with Gambit Dungeon +10.
Please fix it.
Same issue for me, adding on the report as I was told by a support person to do so. Did a Halls of Atonement +10 and did not get an achievement or a portal.
Same here.
No Halls or Gambit port received upon timing a 10.
Just played +11 (in time) and unlocked the achievement and also the dungeon port. 
I did both on 11 too and still haven’t gotten the dungeon ports.