Office Debug: Office add-ins are not displayed correctly in Outlook
Recently one of the ISV app developer reported that after they update Microsoft Outlook to version 1809 (build 10827.20181) or later versions, data from some Office add-ins may not be displayed correctly or may be missing from the user interface of the add-in within Outlook. Specifically in their case, they used IE Control hosted in Outlook Custom Task pane, which is not displaying correctly and missing user interface of the addin. During deep dive we noticed that this problem occurs because a change was made to Outlook version 1809 to enforce Internet Explorer 10 browser emulation. So we documented the changes in the Microsoft KB, published the developer guidance/workaround to move forward.
Hope this helps.