I made relations in the User Collection to the Droit Civil Collection and in the Droit civil collection to the users. It used to work (see a copy of the app below).
This has one major consequence as I understand : when the user leaves the app and comes back again, if he clicks the button he will arrive to a blank screen. He has to log out and log in again to use the app which is definitely not appropriate.
I read this might be due to the use of the data from the same collection (Droit Civil) in 2 different lists on 2 different screen but is solved apparently by adding a nav bar (which I did)