Hi, Sebastián.
Sorry you’re experiencing this issue.
The wp-admin Attendee Report screen can sometimes suffer such performance issues when there are many tickets/attendees for a single event, and our developers have it scheduled to be improved in an upcoming release (likely a couple months at the earliest, and we don’t give ETAs).
This thread should receive a reply once the applicable update has been released. I cannot guarantee when it will be fixed as it’s in the development team’s hands.
I apologize for this issue and appreciate your understanding and patience.
Please let me know if you have any follow-up questions on this topic.