Check out the synchronize function detailed at the bottom of this page:https://www.zonbu.com/doc/doku.php?id=manual:files_and_storage&s=synchronize
I believe this is meant to take care of the problem you are running into. I'm pretty certain this worked for me when I tried it.
It does not answer my continuing complaint about files listed on my Zonbu going missing on-line. For example, I loaded an album onto my Zonbu and a week later went to play back the album and found one track missing. It was listed with the little red square, but it was not in on-line storage. Zonbu Co would blame me for this, but I honestly cannot recall doing anything to cause this problem. I know procedure that will certainly recreate this, but I did nothing along those lines in this case or in the several other cases where files have gone missing.
This I fear is a major fault with their synching scheme from the Zonbu to on-line storage. Do not trust files you put on you Zonbu to be there when you want them.