If you have clicked "open all" and only one document has opened, the default setting of your browser has blocked multiple tabs opening at once. There are two solutions for this issue.
When you click "Open All", you should see a pop up on the top right of your browser window as shown in the screenshot attached above.
If you do, follow the listed steps below.
1. Please select 'Always Allow' Option
2. Select done and refresh the browser to take effect on changes.
On your computer, open Chrome.
At the top right, click More > Settings.
Under "Privacy and security," click Site settings.
Click Pop-ups and redirects.
At the top, turn the setting to Allowed
Add a site (see screenshot)