Not getting results from entity reference autocomplete

Using views 7.x-3.7

I have two content types, one of which is an entity reference of the other.

I've created a few nodes of content, both parent and child nodes, and a view that lists the parent nodes with a relationship based on the entity reference field.

I installed the Views Autocomplete Filters module, and added a "Content:Title" field as a filter to the view, and used the relationship with the child content type, exposed the filter, and selected the "autocomplete" box that the module provides.

I see the autocomplete form element, and it appears to displaying correctly, and when I type out something in the box, I can see that the front end sends an ajax call, and the response is displayed beneath the autocomplete element (no results).

I used the string 'test' inside the title several of the child nodes (ie, "test child 1", "test child 2"). This is also the search term I used in the autocomplete box, which should match up with the referenced nodes, but I'm still not getting any results.

I flushed all caches, re-indexed the site, ran cron a few times to bring the index to 100%, and still no results.

Traced the ajax call to:
/autocomplete_filter/title/[view name]/page_1/test

The message that I get back reads as follows:

{"":"\u003Cdiv class=\u0022reference-autocomplete\u0022\u003EThe \u003Cem class=\u0022placeholder\u0022\u003Etest\u003C\u002Fem\u003E return no results. Please try something else.\u003C\u002Fdiv\u003E"}

Is there something I have done wrong here? I tried using the field itself rather than the title of the entity referenced, but I'm not seeing an autocomplete checkbox.

Please not that, on the node edit screen, the entity reference autocomplete field (provided by the entity reference module) is working correctly. (ie, the path "/entityreference/autocomplete/single/field_spice/node/recipe/77/test" returns the correct results).

Am I doing something wrong?

Please note that I modified slightly the return text (at the end of the views_autocomplete_filter() function in the file " views_autocomplete_filters.inc" from "The %string return no results. Please try something else" - still in the dev, BTW - to "%string returned no results").