As you may know, some players encountered the black screen problem at the end of the game. After numerous tests and checking through our scripts, we were still unable to reproduce the problem.
This seems to happen only to some players. We do not know how many players are affected by it. Since each ending is tied to its own achievement, we decided to disable them in hope that the black screen issue can be bypassed. This way, players can at least see their grades at the end of the game.
We apologize for doing so until a solution has been found, and appreciate your patience for the time being.
Update: Other than the endings, all other achievements can still be unlocked.