Hi. I experience the same flicker when using the Twitch app on my Android TV.
I have different Android TVs/Chromecasts and have the same issue on all of them.
When watching a stream every few seconds it flickers. The screen goes black for a few milliseconds. It doesn't happen during adverts only streams.
Reducing the source resolution makes it flicker less. But then it's blurry.
Casting the same stream doesn't have the issue at all. It's only when viewing the stream directly through the app. I have also noticed it happens if using a Web Browser and the twitch web site on my Android TV rather than using the Twitch app. Only casting doesn't cause it.