Unfortunately the API is being overrun by crawlers. Response time is getting worse and worse. So are the success/failure rates. The API is being hosted on Dreamhost's shared server plan, for which 1 new article per second is simply too much.
While it lasted, it was my pleasure to provide you with this free service. You can get in touch with me via email (firstname.lastname@example.org) or @mmackh.
Grab an open source copy from https://github.com/mmackh/Clear-Read-API