Theoreticaly, we think it's imposible but we'll check your case because you told you see it twice.
To do that, we need detailed info including followings.
1. The firmware version.
2. Model info of your HDD
3. The OS of your PC
4. File size and file count in that folder.(If possible, send us one image file)
5. The name of the preview SW.
6. Directory structure of your HDD(You can snap shot it by pressing Alt+PrintScreen. Paste it at MS Power point)
And finaly let us know the procedure to generate the loss of file case.