Passenger forking with Nginx, action cable & redis

I have some problems on my real time notifier with Passenger (v6.0.0) and Action_cable on my staging server : when i do some action linked to action_cable, some new passenger process appear (forking...) and my memory consumption increase and do not go back down.

My routes config :

mount ActionCable.server => '/user_notifs'

My Nginx config :

location /user_notifs {
        passenger_app_group_name phusion_staging_action_cable;
        passenger_force_max_concurrent_requests_per_process 0;
}

My cable.yml

staging:
  adapter: redis
  url: redis://localhost:6379/1

On my htop, i have like 30 process like this :

Passenger AppPreloader: /xxxxxx/curent (forking...)

Can you help me ? Thank's