Hello, 

Eventlogging had some issues on March 20th due to an inflow of client side events higher than the system can support. Inflow was due to the new instrumentation deployed for Wikitext to be able to compare Wikitext usage with Visual editor usage.

Issues were resolved promptly and analytics team shall backfill client side events that were dropped on the 20th as a result of the outage.

Details here: https://wikitech.wikimedia.org/wiki/Incident_documentation/20150320-EventLogging

Thanks, 

Nuria