SYMPTOM:
in Strategy 2019, “The project can’t be loaded because it is not fully offline, please check whether there is any job running against it or any user session connecting to it. “occurs during unloading a project via Command Manager or Developer when there is user session or job execution.

REPRODUCTION:
CAUSE:
This is working as designed with Strategy Intelligence Server 11.0 and above.
Strategy Intelligence Server 11.0, the project unloading progress is enhanced by enforcing the project to be complete offline before loading the project to avoid scheme inconsistency issues in cluster. If there is still a job running in that project, project will not be unloaded completely and stay in "unload pending" status.
ACTION:
Cancel all the jobs and disconnect all the user sessions which are connecting to the project before unload the project.
To cancel a job from job monitor:

To end a user session from user session monitor:

If the project stays in "unload pending" status for a long time, this action can also be done in job monitor and user connection monitor to let the project unload successfully.
Article Reference Number: KB482889