attachments are not synced for most of the references in Endnote web

I’m using the latest Endnote X8. However, it seems only the attachment of a few references are synced and uploaded to Endnote web, quite a lot of the references’ attachments are not synced.

May I ask if the first time to sync and upload local library to Endnote web will take quite a while?

Thanks!

Yes, It could take hours.