EventLogging suffered from performance problems from Tuesday 2015-05-05 22:00 UTC to Wednesday 2015-05-06 20:00 UTC (22 hours).
During that period, an exceptional amount of events were sent to EL server for MobileWebSearch schema. The system could not handle them properly, and this caused data loss (30%-40% during the period) and some small gaps in the db. All schemas were affected.