The vertical scroll bar missing on Knowledge page on UI15 after upgrade

Issue Description:
The vertical scroll bar is missing on Knowledge pages (Self Service/Knowledge, Service Desk/Knowledge and Knowledge/Home page) after Upgrade 

1. On Support Lab OOB instance
2. upgrade the OOB instance
3. Go to Self Service/Knowledge, or Service Desk/Knowledge or Knowledge/Home page
4. There is no svertical scrollbar on right so the customer cannot see the full page of the content

Expected behavior: vertical scrollbar on the right side if the content is more than screen size

Actual behavior: no vertical scrollbar on the page

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