Well, it's different some of the time. At the moment, this latest crash just now, the midi does seem connected but there's no audio sounding. (If played from the real or virtual keyboard). I don't recall the exact details of last night, just the new crash this morning. Last night I seemed to get it working by simply playing some other tracks, one track worked and it seemed to activate all the others. To be specific I had a flute track that wouldn't play. In DP I selected a brass track, it played, then the flute and all other tracks started playing.
This morning, a new crash, restarted everything. It's all connected, midi seems to work but no sound. Turning the audio engine on and off, and disconnecting, reconnecting, makes no difference.