The player is trying to crawl up for information from the top level frame, which is blocked by CORS policy (IFrames are considered a cross-origin resource, as they are a completely separate document context). If I could get to the page you were on, I might be able to pinpoint the root cause through the client.js and player.js files.
Unless these errors are causing site performance issues (Failing on setting document.domain is really cheap, so I doubt this is causing performance issues), then you might be able to move on to continuing development in other areas. It is worth noting that Twitch isn’t the only frame resource that will do that. Depending on your browser (Safari is really…really bad with reporting this, whereas Chrome, FF and Edge are pretty lax on reporting this), you will see hundreds of thousands of these on any website running remnant advertisements. It is worth noting that this error is not associated with bandwidth costs either, so the user impact, again, assuming there is no performance degradation, is completely negligible.