Hi @顺东 蔡
Welcome to Q&A forum ~
Are there many comments on a page?
- If so, this may causes comments collapsed, I suggest you go to Advanced Track Changes Options dialog box, increase the "Preferred width" measurement for balloons.

- If there are few comments, I suggest you copy document content, minus the final paragraph, into a new document.
Then, please check this issue again.
(To show/hide paragraph marks (¶) as well as other nonprinting marks, click the ¶ button on the Home tab.)
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.