Sorry it took so long to get back to you. The current version of the theme does things correctly, but based on the changelogs, it appears as though older versions may have not. You appear to be using a child theme, so I was saying that a file in the child theme, if based on an older version of Presso, could be overriding changes made to the way author links were generated. If you want to create a zip of your child theme and send it my way, I can tell you where to send it and take a look.
The other possibility is another plugin interfering with the hooks used by Edit Author Slug. You can try disabling all plugins, except for Edit Author Slug, and see if that changes things. If the author Permalinks work correctly, re-enable the plugins, one-by-one, until the author links break again. Then you’ll know the culprit. Let me know the plugin causing the problem, and I’ll investigate why.
If none if the above are the problem, then there’s likely some bad logic, somewhere, in my plugin. I’m not ruling it out, but you’re the first report I’ve heard with this happening, and my testing never came up with this issue.