Often times, as user I start the import of WSDL based or REST (with new one, or old with file and URL selection) service and go through the wizard, something does not work right. So, I typically remove the models generated, and then try the import process again. However, next time when I select the same connection profile I created before, I very seldom get same results. If I restarted the Designer for any reason, the previously created connection profile for sure does not work.
It seems to me that, designer stores a temp XML/JSON file from where it starts processing, during the restart that gets deleted and import process instead of sending another request for the results document it fails with arbitrary error. There is no way to recover form it. IMO, REST and SOAP needs to be treated differently from XML File type sources and issue the query to get response document, not store it anywhere.