Need help for my users!

We have built and published over 600 courses in Storyline. We publish them to our LMS. We include HTML5 output. No mobile right now.

Output options LMS: Scorm 2004

Report status to LMS as: Passed/Failed  (through testing we found out this worked best with our LMS)

Our courses for the most part seem to work ok. Users take the course, take the test, close out. If they pass, the score is in the LMS and they can access a certificate there. If they fail, the score is there but no certificate. 

We are getting calls from users (more frequently now) that users are taking courses and passing, but the LMS records the status as Incomplete. The appropriate test score is there, and we can even see the test questions and the answers the user gave. 

On the results page, the user only sees the grade they need to pass and the score they achieved. The bottom half of the screen is not showing for them. 

Another odd thing that we are seeing is in the test. Each of our slides has a variable written into it to show "Question x of y" and "x" should be +1 as the slides advance. For the users who are having issues, x=0 the entire time. So each slide will say Page 0 of 12 and never advances. 

This is not happening for all users. And it's very inconsistent. Some users can see the course and test just fine and their score reports to the LMS giving them a completed status with the certificate. While others take the same course and pass the test, but the test questions always show 0 and the last results page isn't complete. The user's score will report to the LMS but the course still shows incomplete with no certificate. 

I have tested the courses in the Scorm cloud and see that it's sending the correct data.

I have a feeling there are certain settings within the users' computers that are causing the problems. We have had much better luck using Firefox and updating to the current add-ons of Shockwave for Director, Quicktime Plug in, Adobe Acrobat, Silverlight, Shockwave flash, and Java Platform. 

Is this a good list? Are there others that we should have users installing in their browser? Do certain browsers work better than others? 

We were smooth sailing for a few months, and lately we have had too many customer service issues. We need to figure out what's causing the problems so we can get back on track. We don't want our customers to have to call us every time they complete a course and have us change the status. 

Any help would be GREATLY appreciated!