Why does mail appears to be missing when a new OWA session displays the view of the folder that was used last in an earlier session?

When users login to OWA they may see the content of the last accessed folder as their Inbox content, this may cause confusion for the users. A workaround allows the Inbox folder to be set as the last accessed folder for all connections.

For more information refer to https://support.microsoft.com/kb/817203/en-us