There's a discussion on the English Wikipedia at WT:DYK about "Mark this page as patrolled links" appearing inconsistently on nomination pages. It seems that the cause is a change I made that causes nominations to transclude a new template I had created. It seems that the pages where the links appear are ones that contain the new template, and the link does not appear on pages that do not contain the new template.

The following examples have been found so far:
Luna 2 - created July 11, has new template, has link
Valentina Tereshkova - created July 12, has new template, has link
Mae Jemison - created 5 June, does not have template, does not have link
https://en.wikipedia.org/wiki/Template:Did_you_know_nominations/Bank_of_England_%C2%A3100,000,000_note - created 11 June, does not have template, does not have link