We have experienced a number of anomolies, including this with a particulear SCORM Module.  The particular Module is utilises Flash throughout and we have found that depending on which version of Flash they have running on their computer impacts how much information is sent back to Totara.  In extreme cases, we have found that the final SCORM completion string is not returned to Totara and it never confirms they are complete.   However, once the user uses a different computer with a different version of Flash on it - it works fine.

We have asked users to stop using Chrome for this particular Module to as this appears to cause the most problems.