I'm using https://www.mediawiki.org/wiki/Talk:Sandbox as an example, but it's not specific to that page.
This can be reproduced either by:
- Patiently dragging down the scroll bar until you get to the end.
- Turning off JS, copying the "Load more" link (blue button next to a page) link, changing 10 to 100 (the max), then opening that in a new tab. Continue opening the Load more in a new tab (you don't need to change the 10 after the first one). That means the first page is 10, the next four pages are 100, and the last page is currently 36 (446). It's not an even 500 because of moderation, I think.
The page has 972 topics:
mysql:research@x1-analytics-slave [flowdb]> SELECT COUNT(*) FROM flow_topic_list JOIN flow_workflow ON workflow_id = topic_list_id WHERE workflow_wiki = 'mediawikiwiki' AND workflow_namespace = 1 AND workflow_title_text = 'Sandbox'; +----------+ | COUNT(*) | +----------+ | 972 | +----------+ 1 row in set (0.17 sec)
This is a consequence of the offset being done purely within the index, AFAICT: