To fix the issue of the CK - Express tab on a student chromebook:

Go to Google Chrome settings:

• Click the ellipses, the 3 dots in the top right corner of the browser
• Scroll to and click on Settings
• In the left column, click on Privacy and Security then click on Clear browsing data
• Click on the Advanced tab, scroll to and make sure the check box is checked for Hosted app data, click Clear Data
• Shutdown CB and restart.