Around 11:15AM MT on December 21st, one of our system’s cache holding data for the uniqueness of engagement stats was disrupted, causing a small portion of unique engagement stats to appear inflated. This impacted unique open and click statistics in the Stats API and our Stats pages in your account. Event Webhook data was not affected.
Our team has replayed the uniqueness data and have restored the correct levels of uniqueness for the effected open and click stats. We sincerely apologize for any inconvenience this may have caused. If you have any questions, you can contact Support at https://support.sendgrid.com