Xbox Can't progress - ground missing, excessive loading

Played through once with no issues. Started a new playthrough, and the game is now unplayable.

I noticed someone else posted about this, but the post seemed to have been ignored, so I'm posting again.

Loading times in and out of cutscenes has become excessively long. The screen goes blank, and it seems as though the game has frozen or crashed, but then after 30-45+ seconds, it will eventually load. This is frustrating but not game-breaking.

The most serious and game-breaking new issue arose when starting The Smuggled Relic Case quest. Upon travelling to Dock Town, in the opening cutscene and convo, the cobblestone streets of Minrathous have vanished, and Neve and Rook are walking on nothing. As soon as the quest loads to following Neve, Rook immediately starts falling until they hit an open body of water and die. Attempting to load the most recent save immediately opens with Rook falling again. It's an endless loop. 

No solid ground. The water in which Rook is about to drown is visible.

I can go back to the save right before attempting to start the quest, but as soon as I travel to Dock Town it automatically starts the quest, and the same issue returns. It is now impossible to progress the main story. 

I have tried restarting the game, restarting the console, reinstalling the game.