When you click the Add a region below this region button in the Edit Region menu, you may find that the list of regions extends beyond the bottom of the screen.
You can remedy this by clicking the Allow Scroll of Edit Region Menu link in the Edit Region menu.
You will likely need to close the list of regions to add in order to see the Allow Scroll of Edit Region Menu link.
When you click the Allow Scroll of Edit Region Menu link, the Edit Region menu becomes part of the scrollable part of the page. If you do not see the menu after clicking the button, scroll up. The menu has moved above the area of the screen you are viewing.
Now, when you click the Add a region below this region button, the list of regions will scroll with the page.
To pin the menu again, click the Pin Edit Region Menu to Top of Window link.