When you open a Microsoft Word document in Workspace it is downloaded instead of opened in browser or an empty white screen with the title of the document is displayed.
In the Sharepoint online environment this problem does not exist and the document can be edited online.
The Workspace environment will have one or both of the following configurations:
is NOT using Single sign-on
using an OLD Single sign-on
This is a bug in Workspace.
They are investigating the problem but there is still no solution available.
Enable Single sign-on as described in the following manual: Automatic setup of Single Sign-On(SSO).
When this option is enabled, the users will have to login with the credentials from the Microsoft Office 365 account.
Advise: Enable this option outside Business Hours or in your default maintenance.
Aditional check: Sharepoint settings
Each Document Library in Sharepoint has its own settings. Check if the setting is set to
Use the server default (Open in the client application)