Confluence - Can't sort in page hierarchy by A to Z?

Before I used to see the A-Z symbol when working in the page hierarchy, now I can’t. Why?

The symbol for sorting the pages alphabetically only appears next to the parent page, when the pages are sorted manually in that moment. If you try to re-sort some pages and start again, you will see the A-Z icon then.

More about sorting pages, you can find in Atlassian’s documentation about this subject: Move and Reorder Pages | Confluence Data Center and Server 8.0 | Atlassian Documentation