The 2022/04/28 we were made aware that opens were not properly counted for transactional push notifications targeting the web platform. After an investigation we found out the root cause the 2022/05/04 at around 15:40 UTC and a fix was deployed the 2022/05/05 at around 09:30 UTC.
The root cause was an optimization change in our notification sending service, the new version of the code didn't set some data fields properly. This caused the processing pipeline responsible for tracking opens to be unable to match an open with its transactional group id.
This only impacted the web platform: transactional notifications sent for mobile platforms were not affected. Push notification campaigns and trigger campaigns were not affected.
The faulty change was introduced the 2022/03/09 at around 14:00 UTC and was in production up until the fix was deployed the 2022/05/05 at around 09:30 UTC.