When launching an instance through the Twitch Launcher, with the "open output logs when games start" option set to true, the log displays somewhere around twenty to thirty log lines, then turns completely white, as shown:

I would send Twitch a bug report, but I have a feeling this is more your bug than theirs. I've been wrong about that sort of thing before though.

I have no idea why this happens, or how one would fix it, but it's very strange!

I do prefer this launcher design over the previous, it looks much cleaner, and it's much easier to use.