Outlook and Office 365 have two different types of Inbox, an Unread Inbox and Focused inbox. You need to tell Wavebox which one of these you use so it reports the correct unread badge and notification.
When adding your account for the first time you'll be prompted with different sync options, but if you change which Inbox type you use, or were sure at the time. it's easy to change it later.
1. Open your App settings
2. Find the Inbox Type setting under the mail heading and select either Unread Inbox or Focused Inbox: