alright, found the problem...
the thing here is that the modal fields of the back are loaded and basicly that's correct.
The event-form in the front is having a addfieldpath but for some kind of reason the fields in the backend are getting priority. With 3.3.x the fields in the front were having priority.
what can be done is to remove the addfieldpath but think it's better to rename the fields to venue_front/contact_front and edit the event.xml
maybe it has to with the
but it can also be related to other changes.