Y-disk does not download pictures.

I downloaded y-disk on my iPhone. When I connected the flash drive I gave it access to all my photo, music, and documents. My iPhone confirms the USB. However, when I look at "Internal" photos, all I see are picture placeholders. None of the pictures; except for 2, are shown. The internal videos loaded; however, they will not transfer to the flash drive. I select all videos and it shows that it copies; however, when I look at the USB there are no videos. The bottom line is that the internal show all videos and music. Y disk will not copy the videos or music to the flash drive. The internal will only show two pictures and the rest are place holder showing the date of each photo. The USB photo will only copy the two pictures that show up on the internal photo. This is my second flash drive. Please help.