Nonstop backup files backed up corrupted randomly

I setup nonstop backup to backup my data folder yesterday morning, it ran all day and everything seemed to be OK. Last night I created 6 new psd files in Photoshop in 3 folders, the backup picked them up at 12:xx am and again at 6:xx am. I looked at the files in the backup and noticed that some had 0 k size and some had 64 k; these files are all about 800k more or less. I restored one and tried to open it in Photoshop, it won't open because it was corrupted. I could still open the original files without a problem.

There were some PDFs in the same 3 folders that backed up properly.

The backup ran again at 8:20 am and the same problem still existed. I worked on the files, saved them and I now see that the last backup shows them as backed up correctly with the right size.

Is this a known problem? If so, is there a solution? I would like to see the files backed up correctly the first time around.

I will greatly appreciate your response.

Miguel.