Why aren't my files appearing on my Galaxy Tab 3?

A

AC Question

Files not appearing on Galaxy Tab 3

Hi,
My husband has a Galaxy Tab 3, which he uses mainly to read comics book in cbr files that he already had on the PC.
When he is done reading them, he plugs the tablet to the PC, and copies some more files into the tablet.
Now, the problem is that for the last few weeks when he plugs the tablet to the PC, the folder appears as empty even though the folder is full of files.
I've made sure that "hidden files" can be seen, just in case something has gone wrong, but no, the folders still appear as empty, and he has to delete the files from the tablet once it gets disconnected from the PC.
Anyone experienced a similar problem, and how did you solve it?
Thanks for your help!