I've looked at commonalities in the filenames marked as “unable to sync” and I can state the following:
* The files are in different folders
* The filenames, although different, all happen to have an a-umlaut (ä) in them.
* The filenames, although different, all happen to have two periods in the file name, one separating the extension from the file, the other elsewhere in the name
I'm on OS-X El-Capitan running Creative Cloud 18.104.22.168. I'm pretty sure it was working in the past as the files are from 2013 and 2007.
I have the same problem with filenames containing umlauts (ä,ö,ü) on OS-X El-Capitan.