Question: the resume feature seems to work early in the course but if you quit later, the course starts again at the beginning.
Answer: In this instance, you're using SCORM 2004 2nd edition. The suspend bucket for that spec is rather small (4,000 characters). The course is probably running out of space in the bucket it uses to store data which is what it uses for bookmarking. That would be inline with the behavior you're seeing. I'd recommend republishing as SCORM 2004 3rd or 4th edition.
You can also change the suspend data limit manually in the course properties section of SCORM Cloud. I'd change it to 64000....Screenshot attached.