I am using the search result web part to display the results. But in my case, the document icon is showing but the document preview is not showing. When I further debugged, it clearly shows that the ctx.CurrentItem.ServerRedirectedEmbedURL is null and all other ServerRedirectedPreviewURL and ServerRedirectedURL are also null. I have done full crawl from central admin. Changed the Result type and updated it. Even deleted the display template and uploaded it again. what should I do now?
something happened to your Office Online Server, or Office Web Apps server, you may need to check on the status of that and check the bindings using PowerShell (as Administrator):
On the OWA/OOS server:
On the SP Server:
If either of those don't produce results, then you need to rebuild your OWA/OOS server and connection with SharePoint. You can follow an article here