Files missing which rsync program

Hello everyone,

I ran this command to copy all data between disk usb "sudo rsync -Cravzp --delete-after cp1 cp2" and when I verify the totally on both disk I has difference (almost 10 GB on dimension 50GB). I thought occur a problem and ran another time the same command, but the result was same. I ran diff command and identify the files missing. But what should I do to fix this problem? And why the file doesn't copy to another disk but for rsync program they are there?

Thanks
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