This might explain the unexpectedly low results from the explore similar test. Not saying he fix would ensure usage, but it seems we lost quite a few events. This problem also effects autocompletd data we dashboard, although I don't think we've used it for tests recently. Full text search analytics should be unaffected as they don't use the mw.track functionality.

---------- Forwarded message ----------
From: "Sam Smith" <samsmith@wikimedia.org>
Date: Oct 12, 2017 3:41 AM
Subject: [Analytics] Heads up: mw.track client-side EventLogging mechanism "ignored" certain events
To: "Analytics List" <analytics@lists.wikimedia.org>
Cc:

o/

Prior to Thursday, 28th September, if your client-side EventLogging
instrumentation logged event via mw.track, then only events tracked
during the first pageview of a user's session were logged.

Now, technically, the events weren't ignored or dropped. Instead, the
subscriber for the "event" topic was never subscribed when the module
was loaded from the ResourceLoader's cache and so events published on
that topic simply weren't received and logged.

This bug was discovered while testing some instrumentation maintained
by Readers Web [0] and independently by Timo Tijhof, who submitted the
ideal fix [1] promptly.

-Sam

[0] https://phabricator.wikimedia.org/T175918
[1] https://gerrit.wikimedia.org/r/#/c/378804/

---
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Readers

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