Captivate training buttons not working sometimes

We created a fairly basic training module that consists of 5 slides -- the first 4 have videos on them and a NEXT button, and the last slide is a "thank you" slide.  The idea is that people need to watch all 4 videos to get to the end.  The training is published as a SCORM package in our LMS, and the idea of the 4 videos and the buttons is to keep track of the user's progress through the 4 videos.  The NEXT buttons are placed on the timeline such that they become visible once the video is over.

All of our users are accessing the training on our corporate network using our standard Windows-based firm computers, running more-or-less the same builds of Windows and Edge.

For a small number of users, sometimes a NEXT button doesn't work.  That is, they finish the video, the button becomes visible, but clicking it does not advance to the next slide.  In fact, nothing happens.  For the people who run into this problem, it is not always the same button -- sometimes it's the first one, sometimes it's the second one, etc.  Sometimes restarting the web browser lets the users progress through the training, but sometimes they still get stuck on one of the slides and can't advance.

We've tried debugging the web page but haven't been able to figure out what might be going on.

It's happening to a very small percentage of users, but still often enough to be frustrating to users and to create work for our support team dealing with it.

Any advice would be appreciated.