currently the “Unexpired certificate” statistics diagram https://plot.ly/~letsencrypt/7/ on https://letsencrypt.org/stats/ is not being updated. The other graphs, most notably “Daily activity” are updated daily.
Possible reason: When looking at the Plotly data at https://plot.ly/~letsencrypt/7/unexpired-certificates/#data, all values in the “x” column are formatted like “2016-04-16” but the last one is formatted like “2016-05-04 00:12:11.317137”. Maybe this causes some issue in a parser.
As I have not found any related thread on the forum, I’m unsure if the developers are aware of this issue.