I noticed that some of the countries tend to disappear and reappear on the list.
For example, I saw Vietnam (~90 nodes) and Nigeria (~30 nodes) disappear and then reappear a few hours later. Since they each have more than a few nodes, I doubt that everyone in the country is turning of their clients.
Is there a particular reason for this?
There was a bug - when I sorted the countries by number of connection I removed duplicates! This issue is now fixed.