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: https://confluence.atlassian.com/doc/move-and-reorder-pages-146407727.html