In some cases, outlook can hide certain Folders within the inboxes in certain situations.
If you have custom folders which go missing, what you have to do is as follows.
Right click on the Inbox, and choose IMAP Folders. This will bring up the below dialogue.
Hit Query, to show a list of all your folders on the server. Sleect the folders you wish to see, and then Click "Unsusbscribe", then "Apply". (Some Folders won't do it, such as "Sent").
Once Done, Select them again, and click "Subscribe", then "Apply".
You should now see your folders again in your Mail Client.