Ixpand stops transferring photos

I connect the drive to my phone, I copy files from phone to drive, after getting to aroind half way it stops, when I try again it gives the option to rewrite, skip or keep both of the photos/vids that have already transferred. When I pres skip the files as o would just like it to continue from where it stopped, nothing happens, just says copying files

What can I do? Thanks

do you have icloud photo library turned on?