Do your singers know how the story ends?
When you read a story, there are dozens of little clues that can help you know from the beginning how it’s going to end. the cover art, the blurb, past stories by the same author, the genre, the tone of the opening paragraphs.
You take all this in subconsciously. Without these clues, reading a story can be unsettling. You literally don’t know what will happen next. That unease can lead to a negative impression of the story.
What about the story of your rehearsal. Do your singers know what’s going to happen? You don’t have to hand out your rehearsal plan, but you should have milestones, signposts.
Be unpredictable, but within a framework they understand. Be creative, but not so unfamiliar that they are grasping at straws to keep up with you.
If your singers know, generally, how the story ends, they are more likely to stick with it – and you.