Did you try plugging it back into your desktop to see if the files come back?
Nope, they did not come back.
Try copying them from your desktop again, unplugging the drive, plugging it back into your desktop, and seeing if the files are there or missing. That will eliminate your laptop as a source of the problem at least.
This is what has happened
1. Move files from desktop to portable. Test and they show up. Plug into laptop and only one of the files, a short video, showed up.
2. Move files again from desktop to portable. This time, the files do show up but there is something wrong. They will not play as if there is something wrong. Run the windows drive repair program. Finds errors and repairs.
3. Move files again from desktop to portable but I used a USB 2.0 instead of USB 3.0 port. This time, the file were there and all playable.
What is also strange is that I have no had this issue with the older 2 TB Western Digital portable.
I am wondering if the issue might be in the drive tables.