Hi,
The latest 2.4.7.1. I do use Firebug and there are no errors on the form.
I did see it on the interests field and it is working on that form. However, if I edit article metadata, I get a plain text field. And if I check the source on that page, there is no javascript that would activate that field. I am probably missing something.
I already wrote a plugin that uses an external JSON API and chose tag-it before realizing that OJS is actually loading that by default. The plugin works fine, but maybe it should use the existing tag-it code in some way. But while I do not seem to find that code it is a bit difficult 
The plugin is here: GitHub - ajnyga/jsonKeywords: Plugin for Open Journal Systems. Activates autocompletion in keywords metadata fields and uses an ajax call for the source.