False recursive variable call
Actually, if the environment section define the following
[environment] Args=!-f -n ${Arg_ConfDirectory} ${Arg_Socket} Arg_ConfDirectory=!-c /etc/acpi/events Arg_Socket=!-s ${Socket} Socket=/run/acpid.socket
the execl-envfile fail complaining about execl-envfile: (substitute_env_var(): 210): fatal: recursive call of variable: ${Socket}
The parse process confuse between the variable name Arg_Socket and Socket.