Of course I forgot something 
This time it s the smart_proxy_dynflow_core daemon (run as foreman-proxy too) which need a SHELL env variable
so, override the systemd unit, create a file with /etc/systemd/system/smart_proxy_dynflow_core.service.d/override.conf (or run “systemctl edit smart_proxy_dynflow_core”) with this content :
[Service] EnvironmentFile=-/etc/sysconfig/smart_proxy_dynflow_core
And copy the env file used for foreman-proxy daemon :
cp /etc/sysconfig/foreman-proxy /etc/sysconfig/smart_proxy_dynflow_core