Issue: The current Prefix and Title combination matches another item

Try to visit the title that it claims matches something else and see where it sends you. Check Maintenance > URL Conflicts for existing conflicts.

If the issue persists, please tell me the title so I can test it in my Area Manager.

By the way, the "Prefixes Allowed" setting does not affect the title of the area. If the empty prefix is checked, it means that inside that area you can create pages without using a prefix.

No conflicts were detected.

This is not logical behavior. It seems as if something is broken. Consider to add a few words of text to the tickbox so its no longer empty.

I have changed this checkbox to say "[No Prefix]"

Can you create areas using other titles?

Yes.

Pretend that the area you wanted to make already exists and create the URL manually in your browser's address bar. What happens when you go to it? Does an unexpected page appear? Do you redirect somewhere else?

If other titles work, then chances are, something is there using up that URL. If nothing is there, then there might be garbage in the database from a failed attempt.

Did this problem occur after your most recent import attempt?

Since it only happened for the one title, it sounds like there was already a page/synonym using the title, and therefore this was working as designed.

There was no import in this install. Fresh install and no other pages. No synonyms either.