Thanks, but I have it sorted. It turned out to be some weird browser thing. I’m using Brave browser which is based on chrome. If I opened a private window, it works just fine. If I even switch profiles, it works fine. I even disabled the pluggins (there were only 2), and Brave’s Sheilds up and still have the same issue. So I don’t know what the problem is, but I can mitigate by not using my current browser profile to to develop.
If anyone else has this issue, try a private window.
Ok, after more thinking, I opened the network tab of the request and noticed it was actually a 301 being returned. I googled this for localhost and it turns out that browsers can cache this and will always serve it. So to get rid of it, you need to flush the cache (I actually flushed the browser history, but I think flushing the cache would do the same).
Don’t know why I didn’t think to investigate the network tab first, but live and learn peeps.