intermittent freeze issue in LMS

Hello:

I'm having a problem with a course created in Storyline 360 and uploaded to my company's LMS (Cornerstone onDemand). Hundreds of people have completed the course with no issues, but we get about two calls a week from users who get to a particular slide, which freezes. No one I know (including me) has been able to replicate the problem while using course in our LMS, or in Articulate Preview or Review. For the individual users who are having the problem, the problem often resolves when they try a different computer, or try again on the same computer a few hours later. In one case, we pushed the assignment out to the user through their transcript and that seemed to fix it. I'm wondering if anyone has experienced anything like this ... 

The first problem slide is a drag and drop interaction. Six objects appear one at a time in the middle of the screen, and the user must drag each to one of two targets. Feedback tells them whether they hit right target. The Next arrow is hidden until the user finishes dragging all six of the objects. They don’t have to drag them to the correct target in order to enable the Next arrow – they just need to drag them.

The problem: Some users find that after they drag the first object, no more objects appear. The Next arrow is non-active. They are stuck.

The second problem slide comes right after the first one. In this slide, the six packages enter the screen one at a time from the top, sliding down to settle into two stacks – four objects on the left and two on the right. The problem on this slide is that a couple of the objects appear, and then it freezes.

Both slides have voiceover recordings; the interactivities are not enabled until the voiceover completes.

?