Export/Import feature is broken

I try to import a project I had exported
https://nos-prod-connect.nos.nuxeo.com/nuxeo/site/studio/projects/aescaffre-SANDBOX

and got the following error:

{"entity-type":"exception","code":"javax.ws.rs.WebApplicationException","status":500,"message":"com.sun.jersey.api.MessageException: A message body writer for Java class org.nuxeo.ecm.webengine.WebException, and Java type class org.nuxeo.ecm.webengine.WebException, and MIME media type text/html; charset=UTF-8 was not found"}