As part of the indexing phase, the folder structure is uploaded before the actual file contents get uploaded. This is noticeable especially when syncing large folders (big number of files). Since you mentioned syncing two big folders, the indexing part may not be over yet, so that’s why you only see the folder structure for now. As soon as the indexing phase is over, you will also see files starting to upload.
Sometimes this can also be caused by faulty NAS software, so in order to get a better idea on what is going on in your particular case, I have contacted you by e-mail so that we can do a remote support session.
