Sounds like a bug.

Just only one guess, it comes from Site settings - "Default number of items per page".
If you have it set to 10, then that's it.

But there're no limits in 'Pages' plugin, so it's a bug.

It indeed seems to come from "Site settings - 'Default number of items per page'."

For a quick fix, I changed it to 100, as I don't have that many pages in any of the sections yet (e.g. blog, pages, events). But it's not the best solution.

I'm not sure now if this is working as intended or not. If it's a bug, how/where would I report it?

how/where would I report it?

https://github.com/Elgg/Elgg/issues

You can temporarily fix this adding 'limit' => false to "PagesNav.php"

'batch' => true,
'limit' => false,
'sort_by' => [
   'property_type' => 'metadata',
   'property' => 'title',
  'direction' => 'ASC',
],

I can't reproduce it, all works as expected.

Deactivate all 3rd-party plugins and try again.