What usually is happening and is looked over is only unread messages are displayed in AutoPreview when viewing messages on an IMAP server, by default. To fix this issue you have 2 choices. You can view the message with AutoPreview, mark it as unread or if you'd like to view both read and unread messages, turn on the option to Preview all items.
Outlook defaults to Preview Unread Items using AutoPreview with IMAP servers. Only messages marked as Unread are displayed in AutoPreview. When you open the message the message is marked as Read, and AutoPreview does not display it. To Mark a Message as Unread Right-click the message and click Mark as Unread on the shortcut menu. To Turn On Preview All Items On the View menu, point to Current View, and click Customize Current View. In the View Summary dialog box, click Other Settings. In the AutoPreview section, click to select Preview All Items. Click OK, and OK, to close the dialog box.