https://www.epo.org/en/searching-for-patents/legal/register/documentation/events
Register events
A Register event is a procedural action taken by any party to the proceedings and involving a coding (addition, deletion, change of data) that can trigger an entry in the European Patent Register and the Unitary Patent Register. This entry adds a Most recent event in the respective EP or UP About this file view and also in the respective EP or UP Event history view. For the purposes of monitoring procedural actions to applications, such events generate an e-mail notification to Register Alert users.
Certain procedural actions do not trigger an event. These include changes in file status and certain actions in the appeal procedure.