I got a report today that a Storyline 360 drag-and-drop activity (HTML5) was not registering correct answers. This was from someone using Google Chrome 64 on a Mac. I was able to reproduce this error in version 64 but not version 63, so it sounds like something in the most recent Chrome update broke this.
I republished and the problem went away! I went and looked at the version history for Storyline 360, and sure enough, issues with drag-and-drop were fixed in the most recent 2 releases. So, moral of the story is that if you have courses that use drag-and-drop activities and they were working, you might want to go check on them. They may need to be republished and replaced.