Flagged revision page review statistics (Special:ValidationStatistics) timestamp "The following data was last updated on 17 April 2017 at 08:07. " tells when page is generated. However the data which is shown on the page can be old .
In example Hungarian Wikipedias page reviews statistics says that "The average wait for edits by users that have not logged in to be reviewed is 25 h 59 min; the median is 3 h 38 min. " and based on db average 25.59 has been same from 14.4.2015 and median 3 h 38 from 13.12.2014. The data in percentile table is also years old.
Based on tool labs database case is that in backend stats are updated but for some reason something keeps inserting identical values to database. Bug effects least all Wikipedias with Flagged revs enabled.