All is in the title. I moved my chicken to the new coop before it was finished(an egg was incubating and i wanted a place for the new comer ), hoping it will just say "nope" or else, but instead the game made it disappear or making it unreachable without warning. The night, there was only 7 chicken back home even with my gates open.
It happened that, when the coop is finished, the chicken is finally inside of it. Sorry for the disturbance.