Are you facing issue on author instance where preview of DITA asset is not rendering correctly and this happens on asset details page ? Do you see the html encoding rather than actual page UI - Refer the the screenshot below.
Do you have dispatcher set up on your author instance? If yes, the below solution can help you in resolving this issue.
It could be because of the missing configuration. You should need to enable the mime type for DITA files.
Here are the additional details:
Ditamap and Dita topics shown in Assets UI have to be rendered with Content-Type “text/html”. So to have this work correctly in case a Dispatcher is setup in front of Author, please do following:
Connect server via ssh and browse to httpd.conf and check the path for file “mime.types” file (it could be in /etc/mime.types or /conf/mime.types)
Edit mime.types file and
Search for “text/html” the default value string for this will be “html htm”
Update this string to “html htm ditamap dita”
This will make sure that the ditamap and dita topics are rendered as HTML in Assets UI.