Hi Alex,
A few tips on Basic Duplicate Detection:
You need to make sure you reindex *after* enabling the feature. So, "./dspace index-discovery -b" should be run after enabling the feature in configs.
You need to enable the "<step id="duplicates"/>" step in *every* submission form where you want it to be used. By default, it's only commented out in the "traditional" Submission form, which is only used for regular "Item" objects. If you want to use it for Publication Entities, then you MUST also add that step to the "Publication" submission form.
Once fully enabled, it ONLY triggers in the Submission form when a save of the form occurs. So, in the submission form, after you enter the Title it will *not* trigger until you either: (a) click save, or (b) click on the next step in the submission form (which triggers an automatic save by default).
Tim