Решение: в папке Data\data есть файл размером 1 кб, который надо просто удалить.
На американском форуме есть длинный тред с данной проблемой, перепробовав все предложенные решения по удалению файлов, переустановке баттлнет и отчаявшись, случайно наткнулся на следующий текст:
Stuck at this point too. I’ve spent the entire morning trying to get the game to even repair. I’ve uninstalled/reinstalled Bnet app 3x. I’ve removed my WTF and deleted the cache folder. I’m in a continuous loop of “Oops, something went wrong” and can’t even get to updating the game at all. I’ve gone from the Beta version of Bnet back to the normal version and still stuck in the loop.
[edit 01] the Bnet app won’t update ANY of the Warcraft games from Classic to Ptr to Beta to Retail. They all get stuck in the repair/scan loop
[edit 02] Six hours later and still nothing? Reinstall of Bnet #6 has done nothing.
[edit 03] after perusing other people having the same problem but different games I took a closer look at the data folder of WoW and there it was, a 1kb data file that I moved to my desktop. Instantly, my games started to update with no issue.