This is a small but important fix for all players that participate in the Halloween 2019 event. There was a problem with Steam recording the completion stats for puzzle boxed finished during the event. This patch should fix the issue and let the game start counting your puzzle box completions as it was supposed to, therefore enabling you to earn the 3 related limited achievements.
Unfortunately, there is no way to refund any completions finished before this hotfix has been applied. We apologize for the inconvenience and thank you for your support.