I was certainly not alone in my problem with Screeny recording nothing but a green screen. Interestingly I got the same results from Quicktime, which made me think it was a system issue rather than an app issue.
When experiencing the issue, I was on my (retina) MacBook Pro disconnected from an external monitor. I had been previously connected to a Dell monitor multiple times between then and my last reboot. Based on some tips I saw online, my first step was a reboot which restored Screeny to normal operation.
To test the “external monitor as cause”, I reconnected to my monitor and tried recording on both screens:
– laptop screen: success
– external monitor: success
Then I disconnected from the external monitor and tried again on just the laptop screen: success.
So I have no idea what happened, or how it got “fixed”, but I recommend trying a reboot if you see this issue.