Hi Fujino,
Welcome to the Atlassian Community!
I hope you don't mind me answering in English 🙂
There's currently a bug related to the Calendar Power-Up disappearing from some boards. Our team is working on a fix, but in the meantime, we suggest you try to re-add the Power-Up to your board.
Here's how to do that:
Hope this helps!
Alina | The Trello Team
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