Captivate Drag and Drop slides freeze when loading

My learners have experienced a problem where Captivate drag and drop slides sometimes fail to load.  For most users the slide loads and works just fine. But for 1% of the users, the perpetual "loading circle icon" appears when the drag and drop slide attempts to load.  Once this problem occurs that same user cannot reload the page on any other computer/browser combination including my office desktop computer.  However, if I reset the users progress so they are forced to start over, that user does not experience the same problem the second time around.  This problem has occurred on quite a few drag and drop slides in different courses prepared in Captivate 2017 and published as swf.  Those pages only have a few text items and smart shapes made in Captivate so the slide does not require downloading large amounts of information.  My users see the same problem when the activity is launched from Moodle or Scorm Cloud.  Captivate drag and drop functionality allows me to create very powerful learning interactions and I want to continue using them.  I hope someone can make a suggestion of what I can do to reduce the headache of those slides freezing on loading.