I finally found which component made all that mess :
the stream freeze/gate component from heteroptera is the one !
by replacing them with the “stream filter” component, I finaly have 1 expiration wave after each actualization of my gene pool, thus, only one fitness value per actualization. Now fitness value and gene pool are again linked together !
My coworker just told me he never had this kind of problem with this component. It’s maybe a update or something that create that.
Robert vier (octopus main dev) gave me really cool info about how the all thing work : so check also this post : Octopus : Uncomprehensive results