Hi,
This issue could have occurred due to these reasons
a. If the files are hidden.
b. If the files are lost.
Let's try few steps to resolve this issue.
**Method 1:**I would suggest you to right-click on the External Hard drive and click on properties. Check the size of the drive.
Method 2:
If the isue size of the drive shows correct, I would suggest you to check if the files are hidden or not.
a. Open the External Hard drive.
b. Click on View tab.
c. Put check mark for the option Hidden items.
d. Check if it helps.
Hope this information helps. Reply to the post with updated status of the issue to assist you further.