Snapraid intentionally delete files - why are there errors?

I intentionally moved a lot of files from one folder to another one in my Snapraid setup. The second folder is on a USB disk (which is part of the Snapraid). I wonder why I got error messages regarding the missing files on the next sync. Is there a threshold after which there will be error messages? Because otherwise I would expect an error message for every single file that gets deleted (intentionally). Or is it due to the fact that I moved the files and that I moved them to a USB disk? I already know that due to the USB connection the Snapraid will be unable to recognize moves.