Intermittent Drag and Drop issue

We are having an intermittent issue with drag and drops in 2 exams that we've created. These files were originally created in SL3 and have been working fine for the last couple of years. After exporting these exams from Storyline 360 for this year, we have had 3 users get stuck on the first drag and drop questions they encounter. All the multiple choice questions work fine, but as soon as they get to the first set of drag and drop questions, it freezes and there's no way for them to move forward, so we have to reset the course for them to start over and hope it doesn't happen again. It's not happening for all users, but the issue seems to be increasing. We are not able to replicate it, and it doesn't happen in preview.