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  and independently by Timo Tijhof, who submitted the
ideal fix  promptly.
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