Unresponsive buttons on Control Panel/Site Pages after exiting modal window

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 6.2.X EE
• Fix Version/s: 6.2.4 CE GA5, 6.2.X EE
• Component/s: ~ [Archived] Frontend Infrastructure
• Labels:
  • QA-F
  • ee-ts
  • liferay-fixpack-portal-74-6210
• Branch Version/s:
  6.2.x
• Backported to Branch:
  Committed
• Story Points: 18
• Fix Priority: 4
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal-ee/pull/11411

Steps to reproduce

1 - Go to Admin -> Site Pages
2 - Add 2 pages: Page1 and Page2
3 - Select Page1
4 - Click on "Add Child Page"
5 - Close the modal window without specifying anything
6 - Select Page2
7 - Click on "Add Child Page"
Observed behaviour: Nothing happens. In the Browser console, the following is written:

TypeError: n.formNode is null

Expected behaviour: The "Add Child Page" modal window should open.

Additional Information
Site Pages doesn't use modal window for adding new page on Master.