User upgraded from 8.5.3 to 9.0.1.
After upgrading, the issue occurred in which the mail were not displayed in the inbox in multiple users (it was displayed in all documents).
They executed maintenance task (fixup / updall / compact - D). However, after executing the maintenance task, newly received mails were displayed in the inbox, but the mails originally displayed in the inbox were not displayed.
They confirmed that the mail is displayed in the inbox with following technote, but it was difficult to confirm that all of the mails were restored to their original folders because the many mails in the mail DB.
How to rebuild a Notes mail inbox
As a strong request from this user, it heard that the function of the maintenance task should be expanded so as to cope with such a issue, not the execution of the agent in the technote.