Bethesda have updated their support page for Skyrim Dragonborn for the Xbox 360 and they have addressed many issues in regards to the Sahrotaar section of the content expansion, that is downloadable. This includes the quest At the Summit of Apocrypha, along with a boss fight.
Skyrim Dragonborn DLC: fixes and workarounds listed
Bethesda have said the following so far:
After dying from exposure to the water in Apocrypha, opening some menus causes the entire screen to go black. If this occurs, opening the map will usually resolve it.
After telling Sahrotaar to land, Miraak’s dialogue will not start during ‘At the Summit of Apocrypha’. If you end up in this situation, you will need to reload a save prior to mounting Sahrotaar and allow the dragonriding tutorial messages to finish playing out before telling Sahrotaar to land.
An audio effect from the Apocrypha dungeon Sallow Regent can stack, causing the loop to persist indefinitely. You can resolve this by making a new save and reloading it, or rebooting and loading a save.
Before the fight with Miraak begins, Sahrotaar is frozen while landing during the quest “At the Summit of Apocrypha”. If you end up in with this issue, you will need to reload a save and avoid commanding Sahrotaar to attack Miraak’s dragon allies.
During At the Summit of Apocrypha Miraak is stuck in an ethereal form and takes no damage. This issue can sometimes occur if you make many attacks very quickly or do a large amount of damage from a single attack. If this occurs, you should try reloading a save prior to the issue occurring and try the fight again.
The Elder Scrolls V: Skyrim Dragonborn expansion was released for the Xbox 360 on 4th December this year and it will be released to owners of the PS3 and PC at some point next year. Bethesda launched Skyrim for PS3, Xbox 360 and PC in North America on 11th November of 2011.