I have heard about this problem but it has never happened to me before.

What causes stuck notes? I assume it is a midi problem. So far I haven't seen it with an RT only song. I am using an SD50 hard synth for midi and a Focusrite 2i2 interface as a sound card.
I previous thread said to unfreeze the offending song and regenerate. This seems to work but the problem is happening on several songs and is intermittent so it's hard to tell.
Is there anything I can do permanently?

Thanks
Tony