Unfortunately, I’m not able to reproduce this either 
I’ve even included a not-great-resolution gif below so you can see what I’m seeing. At the end, I check the console for 404s or other errors and don’t see any. A few things I can think of for you to dig in further:
- ask some other people to test the URL for you and report back if they also see 404s
- search the forum for something like “SPA 404”; most of what I see is about the redirect you’ve already implemented, but perhaps you’ll find something else that’s helpful? For example, this post (Vue/nuxtJS slug: 404 on refresh - #6 by jbmoelker) mentions that Nuxt.js dynamic routes need a bit of custom configuration- maybe React routes require something similar, as Tom mentioned?
If you have other suggestions, please let us know.