After upgrading to Moodle 2.3.4 in production here we saw exactly the same issue. It appearently worked fine under 2.3.3. I've backed the mod/scorm directory back to 2.3.3 and it did not remedy the issue. I suspect it might have had something to do with YUI changes. I'm tempted to do a full 2.3.3 rollback and see if this resolves things.