Wrong key in playback.
So I was working with a score, in C Major, but it's played back a semitone flat. I've tried turning on Concert Pitch to see if it had to do with that but it still keeps playing as B Major, I've closed and opened the score again but it still plays in the wrong key.
Comments
attach the score. It's the only way to find out what's happening. You can save part of the score if you don't want the entire score attached.
Indeed, please attach the score. But also check your setting in View / Synthesizer / Tuning and be sure it's set to 440 (or, if you are comparing to an instrumented tuned different, be sure it matches whatever you need it to match).
Edit: Turns out my tuning was at 415 hz.