Hi there,
I have not received my Unit (won on live stream ) Yet, but by chance do you have a Xiao mounted?
I the upload that worked, was it in Windows machine or MAC?
If windows , I would stick with Unplug , hold boot button (white one) & replug into USB,
If it enumerates, great , may need to try it a few times…
for normal boot mode drive available hold boot button while connected and Tap Reset button.
YMMV,
HTH
GL 
PJ