Hi - this is odd, but sometimes when I look at prefs on Codebook on Mac, Secret Agent suddenly stops responding. I have to go into preferences again and reset the SA keystroke to the same thing I always use. Then SA will work fine.
Mac version - 10.11.4
Codebook version - 3.0.4 (345)
Secret Agent keystroke -
Trivia: I use
ctrl-shift-z because I have a Japanese keyboard, and the backslash is under an obscure opt-shift-something-something. The keyboard shows a yen mark where the backslash usually is.