Hi Ben,
I was unable to duplicate the issue you are having. I was able to successfully use your filter verbatim when my field was and wasn’t a subfield in a repeater.
However, the filter: acf/fields/post_object/query is meant for the Post Object type, not the Page Link type. So… it shouldn’t have worked at all for you, subfield or not, if using a Page Link field, right?
Are you able to switch to a Post Object instead without having to change too much else around?
