Why when I copy Xbox captures to external hard drive the captures aren't showing up afterwards?

I recently formatted an external hard drive to back up my Xbox captures to on account of the cloud saves being deleted soon. The drive is recognized as a media storage, and I can even see my new captures on it when I take them. But when I try to copy over the captures from the Xbox network or the internal over to the external, they never show up even if it says the copy was successful.

:)