When Metadata fields are not available in Search, how to fix?

First check in Chrome's console error log if there is an error message where a URL "been blocked by CORS policy: No 'Access-Control-Allow-Origin'" has been logged.

If yes, go the Internet Information Services (IIS) box and update the list of allowed CORS origins in the search API's web.config file. This is usually on the Application Server.

Likely physical path: C:\ONE Discovery\OneDiscovery.Web.API\Web.config

Under <appSettings>, find <add key="contentOrigins" value="" />, set value to to the URL that has been blocked.

If the web.config file already has the correct URL, restart IIS and see if that resolves the issue.