Erratic Behaviour in LMS

We are experiencing a plague of problems encountered by students viewing our Studio 9 courses in Articulate On Line.  They centre around restarting from the exit slide, and on records of activity.  

Quite frequently, even though a student exits using the EXIT button etc,  when Yes is selected to the question "do you want to start where you left" (or whatever it says) he is taken to the first slide.  Sometimes it is then possible to select the last slide viewed, sometimes not.

The courses are set to track by slides viewed, and completion, mainly because they have several interim quizzes and we don't want to try and track those. (Pass is required to move on and eventually reach the final slide). But sometimes the slides viewed is shown in history, sometimes not. 

Any ideas for eliminating these problems? One of the courses is quite challenging and students must take 2-3 breaks while doing it. We are rapidly losing goodwill when they have to go through all the previous material and interim tests twice or 3 times.

And why, on the same course, is the slides viewed shown on one student's history, but not another's?

We brief students to use the EXIT button and log out properly, and they are doing that.

We have also had problems with Abu Dhabi based users; in their case there were problems with Internet Explorer in viewing a course; just a blank page coming up, but changing to Chrome proved better. But even in Chrome there are the restart and slides viewed problems.