I don't use either, but do you have Box set up so that files added to it are synced with your phone? If so I could imagine it creating a second copy of the files on the phone (you copy a file to Box & it syncs a copy back to a folder on the phone).

Apologies if completely off-beat, as stated I've never used Box.

 

when transfer data from mobile to drive or vise versa then it make duplicate copies of original and it store in device as well as consume memory. that's the reason of this error.