If you see a single tab instead of multiple tabs after clicking on the bulk operation option, it is likely that your browser has blocked new tab redirects. If that is the case, please check your browser settings for 'pop-ups and redirects'. If you are a Google chrome user:
- Go to the tab where you performed bulk operation,
- Locate and click on the popup blocked icon from the address bar,
- Select Always allow pop-ups and redirect from <your site>.
For further info please visit the this page.