Calibre on a Mac and chronosync issue with a Synology NAS

Hi,

I have Calibre installed on my Mac.
I want to provide access to the library even when the Mac is off.
So I try to copy the content to my synology NAS and install COPS interface.
I use Chronosync to copy and everything runs fine at first time.
COPS is seeing the books and it's great.

But since a few days, when I add new books in calibre, stop calibre and run the sync task, I dont get the chronosync task to copy the new metadata.db and the new books.

I dont understand why.

Any idea ?