So when I was implementing reactjs in the twitch extension I had this same problem with hosted test, normally this is a problem with dynamic routes, there are a few ways to solve this, one of them is to use HashRouter’s react-router-dom, the BrowserRouter does not work correctly when embedded in the twitch, there is some discussion in the forum about it.
All problems with assets, uploads, routes and webpack (this is very important, its extension is usually refused if you do not change some configurations of the webpack) of the reactjs: