Have tested this in 2.2.2, 3 different ways; Via "Media > Network Stream", RTMPdump CLI, and Livestreamer CLI.
As the title says, RTMP streams will often open with no video track, but the audio track is fine. I can't see any other information about this online.
The RTMP server is nginx with the rtmp module installed. Playing the streams through VLC also seems to add an additional 5 or so seconds of latency to them (no it's not network caching causing it).
I'd appreciate any advice on this.