Aspera download of multiple files randomly creates an error toaster

reproduced in the environment: http://preview.default-pr-54-nuxeo-aspera-connector.jenkins.l2it.35.231.200.170.nip.io/nuxeo/ui/#!/aspera

How to reproduce

• select multiple files
• click on "download with aspera"
• depending on connexion, a toaster is displayed with the following message : 

"An error during Download. Check if the selected files were uploaded with Aspera"

edit : for some testers, the error is systematic

=> Clicking again on download with aspera just after error message will begin the download normally in certain conditions