Nico,
The functionality was removed (or migrated) from Event Rocket with the update that just came out. So you won’t find it any more unless you try an older version.
For those of us who had been using it the coordinates are filled in from the side bar. (As seen in this screen capture that hasn’t been updated yet.)

So when it is updated the Event Calendar takes over the coordinates but the checkbox isn’t checked (so you can’t see them). It still reads and displays the venue correctly so it is just a cosmetic/migration issue.
Hope this sheds some light on the issue.
Glenn.