I had a user with a similar problem this week. IE 11 is no longer a supported browser by Microsoft. I upgraded her browser to Microsoft Edge and she was able to process documents again. I am running DocuWare Cloud 7.3. My user could not open documents from the Document tray nor could she store documents in a file cabinet. Also, she was able to run DocuWare in the current Chrome browser without any issues.
Hope this helps,