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Changes deployed on an emergency basis Friday, 2015-05-22, caused some tagging data to no longer be captured, causing an unrecoverable loss of data. This was feared to invalidate the Visual Editor A/B Pilot test in progress; however, that test used a different mechanism to gather data and was not affected.
This is a step by step outline of what happened to cause the incident and how it was remedied. Please ensure to remove private information.
What weakness did we learn about and how can we address them?
Explicit next steps to prevent this from happening again as much as possible, with Phabricator tasks linked for every step.