The number of pageLoaded events registered by the Popups schema seems only about 60-70% of what one would expect from the corresponding number of (non-spider) pageviews from Hive, see these three charts from the experiments on ruwiki, itwiki and huwiki. It seems worth determining whether this can be explained by natural factors (two possibilities listed below) or points to an issue in the instrumentation.
(Restricted to Firefox-like user agents to circumvent the general EventLogging data quality issues from T146840 .)
The y-axis maximum is selected as the sampling rate on each of these projects, per https://meta.wikimedia.org/wiki/Schema_talk:Popups . NB: the schema samples per browser session, not per pageview, so part of the discrepancy will come from session cookies not being set or preserved. If this is a factor, one would expect the discrepancy a bit smaller when the sampling rate is higher.
As @dr0ptp4kt pointed out earlier, DNT is another factor, but probably not large enough to explain a 30-40% drop.