cannot edit attendee

Hello,
When I check an attendee and click on edit I want to edit his info. but instead it opens a view that looks the same like the add new attendee. how can I edit attendees?

@webfeuerflo: You are in which JEM?

Still running 2.3.3

First of all it would be good to update to JEM 2.3.5
and I hope you are on a actual joomla 3.10

yes, joomla 3.10.11

I made some overrides for the backend view and did not update, because I feared that they might not work anymore (my client wants to see less details in the tables).

I tested it without the overrides and the bevahiour was the same. looks like I will try and update and see if it fixes the problem