I'm not sure why the stream wasn't working. I think there may have been a temporary ban because of non-gaming content streaming. The streampro.io overlay derped out and blocked the TF2 stream.

During the outage, OBS was connected and streaming to twitch but no stream was visible. I didn't have time to investigate, but now it's magically working again. If there was a twitch suspension, oh well, it's fair for them to suspend streams that aren't adhering to the rules/content requirements.