We know that the system is emptying the hopper if there's no more agent logged in to the campaign but leads that came from Workflow Automation stayed in the hopper. 

This FAQ will help you on how to remove leads in the hopper that came from Workflow Automation.

From the Admin page, click on Call Center and then Campaign.

Search for the campaign and click it to go to the settings.

From the campaign settings, click on the Hopper tab.

From the Hopper tab look for "Remove leads with 'WA' hopper source.

Set it to Yes, the system will remove the leads from the hopper.

Set it to No, the system will keep the leads in the hopper.

 Click on Apply Changes once done.