Yeah, weird. I tried using it later for a different composition and it worked alright, but when I tried to do the other one again just now it didn’t work again, so I think it might be this composition or possibly the fact that I’m recording portrait oriented video?
WAIT I FIGURED IT OUT
I appear to have used a “/” in the name field of the syphon server patch which caused the recorder to try and create a file using a / in the name.
(for anyone else that has this derpy problem, you will need to quit syphon and reopen it before it works)