If a job is using a HostGroup and you want the FileList Variable to use the Host from the Job, check the options "Apply task Host" and "Apply task Login" under the [FileList Variable] Variable tab.
From the documentation:
Apply Task Host: This setting deploys the agent of the task accessing the Variable object.
The task's agent is preferred if this option is set. The variable's agent (see Host) is used if the task does not include an agent (such as in Script objects). An error occurs if the variable is to be resolved and neither the task nor the variable includes an agent
Apply Task Login: This setting deploys the login of the task using the variable.
The task's Login object is preferred if this option is set. The variable's login (see "Login") is used if the task does not include a Login object (such as in Script objects). An error occurs if the variable is to be resolved and neither the task nor the variable includes a Login object.
If you have a Promptset that is using a FileList variable as Data Reference, check the option "Dynamic" on the Prompset component's Property.