I think the web client is trying to use the Document Preview Service (aka LDPS) here. This is used for Office documents, so it won't impact pdfs or image documents. There are a few things that could go wrong here. I would start by looking in the event viewer on the server for some details, and the browser's developer tools (F12) might give you some clues about what is not working.

If you don't see anything helpful there, I would suggest opening a support case.