We recently tested using a file_url to apply a template to a number of courses. All courses except for one imported correctly. The one course that failed displays 'file not available' under Settings -> Import Content in the course and the state is 'queued'.
The api call to retrieve information about the migration shows the status as 'running', the migration_issues_url returned shows 0 issues, and the progress_url shows "workflow_state":"queued". Since there was a problem with the file_url, this import will be queued forever and the only way to see why the template did not import is to enter the course manually and look at Settings -> Import Content.
In a case like this, where the file_url did not get passed/received properly, I would expect the job to 1) fail and not be queued forever 2) the API call to list 'file not available' under migration issues found in the migration_issues_url.