Thanks Sync Support, 1. All Mac OS, in the most recent case using two Mac OS 10.8.5 and 10.6.8 -- aha, first clue. I thought they were both running 10.8.5. 2. On the 10.8.5 mac, there are several folders and files in .sync/Archive --I haven't compared the list there with the missing files list. On the older one, there's no .sync folder at all. Think I'll go back up and upgrade the older Mac to something current and try again.