Unavailibility of videoplayer in development rig
Due to the new video embedding structure at twitch, the dev rig is currently not be able to show the videoplayer behind the extensions.
Perhaps I have missed some information, but it could be quiet helpful to mention this (temporarily?) unavailibility somewhere.
And then I saw this Troubleshooting chapter with its Feedback button...
This bug has been tracked on this GitHub Issue: https://github.com/twitchdev/issues/issues/138
Developer Rig version 1.2.6 addresses this issue.