I think 'frozen' is the right word- like a computer screen, only in this case stuck in a delay going round and round. Unplugging and replugging the M9 ( ie re-booting it) worked to get rid.
Or, possibly, I trod on the looper? Mebbe?If I was looping a delay then it would sound the same?
And trying to sort it out mid set of course...:(

