Getting some .Not Completed.s

I am connecting material to Sum Total LMS. The content is performing as it should and overall the communication with the LMS is working. However intermittently we are getting people who complete the training and get a 'Not Completed' within the LMS. This occurs especially with people accessing externally via the web - and I have confirmed that they have completed the training.The LMS vendor and my technical people believe that it is the content that is closing before the LMS can deal with the data. On the final page of the training, the 'Congratulations' page, all I have is the Set Completion action. Users exit via the LMS close button. I have put the SCORM required Exit button on another page and hidden. So I cannot see that the content closing too quickly is the problem, unless I need to put a delay on the Set Completion.I believe that the problem is a broader network issue - does anyone have any other ideas, things I could try or experience with this?