Welcome to the MongoDB Community Forums @Hengfeng_Wei !
Automatically closing topics after a solution has been accepted is intentional to help keep discussion focused and highlight the posts that are most helpful. When a solution has been accepted discussion remains open until there have been no further replies within 5 days. Leaving discussions open indefinitely tends to attract responses which become much less relevant over time, particularly if there are very different software versions and platforms involved (eg “I have the same error message”).
If you have a follow up question (or new ideas/solutions to discuss), it is generally preferable to start a new discussion to keep the details of different environments separate and improve visibility of new discussions. That will also allow you to mark own your topic as “Solved” when you resolve any outstanding questions.
Mentioning the url of an existing discussion on the forum should automatically create links between related discussions for other users to follow.
If you want to suggest reopening, merging, or splitting discussion topics you can also flag a post for moderator attention: choose “Something else” and let us know what help is needed.
Regards,
Stennie