The Documentation tab, in an entry, is empty although you have Reset the layout in the Window tab.
First validate that you are allowed to View documentation in Administration - Vault Settings - Permissions - Documentation - View documentation.
If all is good, it might be due to your server having the IE Enhanced Security Configuration option enabled. This could prevent and block the document from loading. You would need to disable it, but we would advise you to retain the enhanced protection.
Here is a topic with more information from Microsoft