Someone says they sent the meeting details, yet Outlook's visible message list does not show them. With Focused Inbox enabled, incoming mail is separated into Focused and Other. Looking at only one tab can hide an otherwise delivered message from your attention.
Open Other and search for the sender or subject. Also inspect any active view filter, such as showing only unread messages. Focused Inbox organizes the inbox; it is not the same as the junk-mail folder or a rule that moves mail into another folder.
If the message is in Other, decide whether this one message belongs in Focused or whether future mail from that sender should go there too. Outlook offers different choices for a single move and an ongoing preference in supported versions.
If the two-tab system repeatedly hides work you need, consider turning it off rather than retraining it indefinitely. Menu locations differ between Outlook editions. After changing the view, find the same message again. A visible inbox preference does not recall, resend or alter the sender's original message.