As brought up by this comment, there were 6 hacks during the contest but they were not added to the main tests for the submissions during the contest. They are added only for practice submissions (roughly 3 minutes after system testing ended).
Having 6 hacks highly suggests weak pretests, and it is likely that at least a few hundreds of solutions will fail when they are judged with these tests. This could significantly change the scoreboard, and should not be neglected.
We are not late. Error_Yuan, please rollback the rating update and rejudge the solutions.
Fixed. Ratings will be updated later.
Thank you. I'm glad that the issue is properly addressed.
Sorry, after I clicked the "add hacks" button, I forgot to build packages and started system testing. And after seeing your comment, I randomly opened a submission and saw there were 10 tests. (Yes, the package was built after system testing and idk why...). I apologize for my mistake.