We have found that sometimes OSX only gets change notifications when folders change (as opposed to files), so this would make sense if you are copying a folder of media to the NAS.
We get the notification when the folder (and the first few files are copied), but we don’t get an additional notification when the rest of the files copy, so those won’t show up until the next rescan, or until you force it.
We do have some plans to make this better in the future, but for now you can either change the rescan interval or just force it when you copy new media over.
We’ve spent a lot of time trying to work around these issues and we know they’re frustrating, so thanks for your patience @Da_Chen !