since the relaunch of the studio about two years ago, there was a nasty bug that would occasionally render a track unusable. This was haunting us for quite some time now, but we where finally able to understand and fix the issue. If you have such a draft that cannot be opened, please leave a comment with the URL of the track, and we'll try to repair it. You can find the URL at the drafts section on your user page. Cheers!