It means, that it reported zero size on the NAS and therefore won't transfer the files to the laptop. Only when I copied the files to the laptop it index the folder on the laptop and the NAS and the Laptop started to "sync"
I'm already in contact with support.
As for rslsync: there is no rslsync user under the "local user". There is one though under "internal system user" (or what it's called in english). And this user has no access to any folder. And they work fine with my other PC (also they don't sync to the laptop)