Yes I know obviously 737-300 and new airbus are really different
I love also boeing because flight are less borring !
Sorry because i did'nt take screens when the problem happened :/
I made the flight today and found a solution. When Vnav does not get off the plane right away I switch to level change. When I return on the descent path I put Vnav and it leaves again;)
Thank you for the indication of the levelchange it unlocked me!
I don't know if it is a bug or something like that but juste 2 minutes of level change solve the problem