REST API Broken

The REST API is totally broken for 2 blogs of mine. When I use a public API method like https://public-api.wordpress.com/rest/v1/sites/mywebsite.com/posts/ I got this message :
{"error":"token_target_mismatch","message":"The authorization token does not match the API target."}

This method is public and doesn’t need any token. I use it for months without authentication.

The API worked fine few days ago.
My blogs are self-hosted, use Jetpack (2.3.2) and JSON API is activated.

Is someone has an idea ? Has API changed recently ? There is no message about that on the documentation http://developer.wordpress.com/docs/api/

http://wordpress.org/plugins/jetpack/