In short: the app created a second folder ( [removed by moderator] ) because the Box service account it authenticates with may have a different root folder ("0") than the Box user where your original folder ( [removed by moderator] ) exists.
Your files are being saved inside the app's folder ( [removed by moderator] ), not your existing one ( [removed by moderator] ). To find them, look for the service account's content in your Box admin console — it may be listed under "Service Account" or "App User" content depending on your Box enterprise setup.
How do I see Service Account or App User folders????