beginner's mistake?

I have a problem with my dropbox and boxifier. I have a lot of photos and videos in a very large folder that is subdivided into folders on my NAS drive and I want them to be copied via boxifier to Dropbox and from that moment on I want to always synchronize via boxifier. I dragged the folder from the Nas to Boxifier and it started. Boxifier gave the message that it was ready. However, I see that the folders are now in Dropbox but not the files (the photos and videos). What am I doing wrong?

Nothing wrong here, most likely just a slow NAS drive. Please allow me to explain:

Due to the way sync works, the folder structure is mapped out and created first on Dropbox then files are synced to this folder structure. Some NAS devices are notoriously slow. If you see the folders showing up first and files later then please remember that a slow NAS is most likely the cause of it. The only thing left to do in this situation is to have patience for the files to sync.