Can't find drag & dropped files on passport

I’ve dragged and dropped files from a computer I had to return on my WD passport. When the passport was connected to the computer, the files appeared properly copied. However when I now plug the passport on other computers, I can’t see does files. Any clue about what happened ? Are the files on the passport but just not visible?
Thanks a lot.

Are you facing this issue while trying to copy files from other computer in My Passport ?