DAMAGED STILLS FROM BACKUP

I always organise every media inside the FCPX library. I save my libraries on a backup Western Digital Duo 20 TB. Raid 1 for dubbel protection. I use a Cal Digit T3 Thunderbolt for video editing. So for more complicated reediting I copy Libraries from backup to T3. Now I found out that some of the stills used just show up as black. I reveal in finder and I can preview the still picture a photoshop .psd as normal, so the picture is there. I open the stills in photoshop and resave under a different name, import to FCPX it doesn't work.
I have to make a new project in photoshop copy the picture from the damaged file which actually works and import that.That works fine.
I also opened the library directly from the backup disk, the photoshop stills were OK.
I copied the reedited library out to the backup again opened it from the backup and the stills where damaged again.
I zipped the library file and copied it to the backup disk the stills were damaged.
Anyone else out there that have an idea what is happening ?

I can't speak to your specific issue, but I have found that .psd files are a bit of a pain in FCPX so I always try to convert them to .png files and work with those. I've never had trouble with a .png file but I have had other issues with .psd files.

Best of luck!