I'm using Windows 10 and just tested this on latest versions of Chrome, Firefox, and Edge browsers. It worked correctly on all (although clunky and slow on Edge.)
I put this up on AxShare here: https://bope9k.axshare.com/
I tested it with no problems on Windows and Mac (OSX Sierra) with Safari and Chrome.
So, looks to me like this is a bug in the Mac version of Axure.
See the version posted earlier in this thread: Horizontal_DragandDrop_reorder 2.rp and the discussion about the use of "This.property" versus a local variable. I thought I had started with that version, but I guess I did not. You should be able to update my code fairly easily by following josephxbrick's instructions in this thread. Let me know if you still need help with that.