This export will run in the celery process - can you check that the service is running?
$ cchq <env> service celery status
And if so, check the service logs to see that the task is received, and whether there are any errors reported.
$ cchq <env> service celery logs
The task should be in the default celery_celery queue (the log file will contain that in the name), and the task is called export_ucr_async. You should see a line in there like:
Received task: corehq.apps.userreports.tasks.export_ucr_async
I'd also check the main commcare process logs to see whether it reported any issues queuing the task.