This field appears to have gotten lost at some point:
SELECT DISTINCT event_pageTitleHover, COUNT(*) FROM log.Popups_16364296 WHERE DATE(timestamp) = '2017-05-01'; +----------------------+----------+ | event_pageTitleHover | COUNT(*) | +----------------------+----------+ | NULL | 60407 | +----------------------+----------+ 1 row in set (1.20 sec)
Probably also applies to namespaceIdHover.