While reviewing views to special pages for T234559, I noticed that views to a number of commonly viewed special pages such as History, Watchlist, and Contributions are not being recorded in the pageview_hourly data starting around July 23, 2019, leading to a sharp decrease in the daily number of views to special pages at that time. See plot below.
SELECT CONCAT(year, '-', LPAD(month, 2, '0'), '-', LPAD(day, 2, '0')) AS date, access_method, SUM(view_count) as special_page_views FROM wmf.pageview_hourly WHERE year = 2019 AND month >= 06 -- look at special pages AND namespace_id = -1 AND agent_type = 'user' GROUP BY access_method, CONCAT(year, '-', LPAD(month, 2, '0'), '-', LPAD(day, 2, '0'))
A review of the top viewed special pages on English Wikipedia in July includes the commonly viewed special pages but the list appears much different for the month of August. See top 15 for each month below.
July 2019 Top 15 Special Page Views
SELECT CONCAT('https://en.wikipedia.org/wiki/',page_root), SUM(view_count) AS views FROM ( SELECT IF(INSTR(page_title,'/')=0,page_title, SUBSTR(page_title,0,INSTR(page_title, '/')-1)) AS page_root, view_count FROM wmf.pageview_hourly WHERE year = 2019 AND month = 7 AND namespace_id = -1 AND project = 'en.wikipedia' AND agent_type = 'user') AS pr GROUP BY page_root ORDER BY views DESC LIMIT 50;
August Top 15 Special Page Views
I reviewed webrequest data as well and confirmed that access requests to all typical special pages are being recorded as expected; however, when you filter by is_pageview there is a similar drop in views on July 23rd and a change in the top viewed pages as seen in the aggregated pageview_hourly data.