Bi-weekly I help with writing down the Area51 statistics of 2 beta websites in this Meta Sustainability SE post and this Meta Martial Arts SE post. We do this so all site users can monitor growth of these sites.
Today I noticed that both the 'visits/day' and the 'total users' statistic in Area51 did not change for both sites since at least May 15, which seems very unlikely especially when it happens to 2 sites at the same time. Also the statistics in the 'site stats' box on the homepage of both sites show different visit/day and users numbers than Area51, so it seems new statistics are being generated but just not updated on Area51.
A quick look at other beta websites like Genealogy, Gardening, Politics and DevOps shows that for all the 'total user' Area51 stat lags behind the one reported in the homepage 'site stats' box, so all Area51 beta-site pages are probably affected by this bug.