Problem Copying multiple files to USB

Copying files completes but some files are unreadable and some folders have no files transferred in them.

Attempting to copy a set of files from my Hard drive to a NEW usb thumb drive. I have used several usbs thinking it was a size issue. First units tried were 2 terrabytes, then a 128 gig. The asus x200ca running on windows 10 home 64 bit with 4 gig RAM will take hours to copy all the files and folders. Initially everything appeared good on the large drives but the files in the folders did not copy. I did this several times with the same result but copying each folder does work. Trying again with the 128 gig USB, the files and folders did appear to transfer but about 70% through the process something seems to have changed as all the files after a point are not readable.
I have since tried again with the 128 gig drive formatted in NTFS with a similar result.
Net result, 8 gigs of data in 20 folders and 1900 files including pictures, varying degrees of results and no confidence that I got it all and it is useful.
What am I missing here? I was fine until I got into larger drives with exFAT formatting.

I use my USB as a portable file cabinet for my work data and need a simple backup in case it gets damaged or left at a location. I need to re-synch often so both sets of data are current.
Is there a better way to do this and still be pocket portable?
 
Can you start over by reformatting the thumbdrive?

My favorite program for this is Allway Sync which can be used to reperform the copies in differentical mode(only changed files gem moved)

Hi volumes of COPY can consume too much memory and thus become unreliable.

On the reformatted USB, I create a root level folder (Backups) and then using Allway Sync, create a job
on the left side MyDocuments on c: to the right side Backups on the USB
 
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