16GB Cruzer having disappearing files problem

None of the files are over 1GB… the MP3’s are all under 10MB or so. None are set to hidden. They have all been scanned with the systems AV program multiple times and it didn’t find anything. I can try turning off the systems AV protection before copying but it hasn’t been giving any warning when i copy the files. I have successfully copied the same files specifically to the drive that have at othertimes disappeared when i copied them with a larger number of other files. IT just seems like once i go over the 5GB or so amount it randomly has the folders that start showing empty. Many times they are the last set of folders in the list alphabetically. IT really has me stumped. Especially since i’m seeing it happen on two seperate computers