In your screenshot, it’s not obvious what your ranking formula is, and it’s really important to configure properly:
By default, custom ranking is only one criterion among the ranking formula, and not the first one. Which means that textual relevance, or geo distance, for example, will be considered first before your custom attribute. Only records that rank the same for all previous ranking criteria will be sorted by custom attribute.
To make sure results are always sorted by descending alphabetical order of their title, please make sure that
desc(Title) is the first criterion in your ranking formula (not just in the custom ranking).
What does in mean in practice? In your dashboard, under the “Ranking” tab for your index, in the “Ranking Formula” section, “Sort by Attribute” should be enabled.
Please let us know if this works for you!