Course completion message triggering early

We have courses created by an external vendor, published as SCORM 1.2. I don't know how the courses were authored. (Looks like xml, js and css?) They have been unresponsive to this issue. We use Cornerstone OnDemand LMS. 

Scenario: I had already completed all items in a curriculum. It was force assigned to me to make me start over as if I'd never taken it. In this newly assigned curriculum that I had not started yet, the first module showed Registered status as it should (not In Progress).

When I launched the first module, it had a button available asking if I wanted to “Return to last visited page.” Previously, this button only appeared upon return to the courses that I had already opened.  It sounds like cookies are involved. We cannot expect learners to clear their cache before attempting a module again.

The main issue we are experiencing is this popup message that appears on many of the screens as we progress through the module, "You have completed this course. Do you want to exit or resume?"  This pops up even in this module that was newly assigned to me and has never been launched. It seems to appear only on the screens that have elements that require the learner to click or interact with before they can click Next to move ahead.

I'm still testing but it may be sending the completion data to our LMS prematurely. 

Could the vendor be using cookies for bookmarking instead of SCORM code? Or what else might be happening?   Thank you for any guidance. We need to have a better understanding of what could be happening before we approach the vendor for the umpteenth and last time. -Jill