Files Disappearing on MyBook 4TB

Files are disappearing from my MyBook. The MyBook is connected to my router so I connect to it over the network. I copied pictures from my PC and phone to my MyBook 4TB. The same day, I used the pictures in an application so I know that they were there. I also could see them in the directory list. The next day I rebooted my PC and try to look at the pictures and the folders I created and the pictures were not there. I tried recovery software, but I had written additional files to the drive before I realized they were missing so I wasn’t able to recover anything. I have run the WD utility and it doesn’t show any error on this disk but I am afraid to continue using it. Is there a limit to the # of folders/files in a particular directory? What could cause this behavior?

One other piece of information - when I look at the properties of the top level folder - the space indicated is several GB larger than the space in of folders/files. I have checked for hidden files, etc and still can’t see this data. The data itself is not that important, but I don’t want to lose any more data going forward. The drive is only about 10% full (~400 GB out of 4 TB).

Hello,

Are the files disappearing from the external drive or the computer? Can you please send some screen shots of the backup tab on the software.