Middle C wont release

When I play middle C and then come off the keyboard it continues playing. This is not a keyboard problem as it happens whichever key I put Middle C on. (For example if I transpose or move the octaves) and if I use a different keyboard. Also my keyboard works fine on a friends system. Very frustrating! Its a recent problem and has worked fine in the past. I was experimenting with quick controllers when this first happened but cant seem to pinpoint the problem to that. Thank you for your help.

First step would be to use the MIDI Monitor Insert to see the exact MIDI messages the track is getting.

Make sure you don’t have the Input Transformer messing with the input data.