I still have my 2004 Creative Zen Xtra mp3 player (40gb). I use it with a mini-amp connected to two 30 year old speakers.
Drag and drop of folders works totally OK for me between my Win 10 laptop and my Clip Sport. I usually do not use 2 open file transfer windows. Maybe try it using the Clip Sport Music folder on the left side of one file transfer window as destination?
And your file source folders are on the right side of the file transfer window.
Also. Maybe try only a few folders at a time? And make sure you use the “Eject device” feature in the Win 10 tool bar.
