I am trying to create a new external content type using SharePoint Designer, whenever I am trying to add WCF connection I get an error message as "Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information"
To troubleshoot the issue, check things below:
Close and re-open the SharePoint designer.
Clear SharePoint designer cache according to the article below.
- If the issue still exists, you could re-install the SharePoint designer.
Updated: I suggest you could submit a service request like the picture below.