Drag but no Drop on Mac

I've created a course with a freeform drag and drop question.

• The 8 items appear one-at-a-time and the learner must drop them on one of two rectangles (do and don't).  If dropped incorrectly, the item snaps back to the original spot.
• I've published it for an LMS with the fomat "HTML5 with Flash fallback and AMP"

This works as designed on a PC, but not on a Mac.

Using a Mac, the item snaps back if incorrect, but when placed on the correct drop target, the user is unable to "let go." The item can't be dropped.

I've tried both Safari and Firefox as the browser on the Mac, but with the same issue.  As a work around, I added a next button, so Mac users can move on, but they'll never see more than one item in the interaction.

Has anyone run into this?  If so, how did you correct it?