I agree, would be good to know if by erratic you mean performance or backstage behaviour etc. At least from a front of house/audience perspective, CZJ actually achieved quite a lot in Night Music - she was clearly a draw who could bring in the crowds to pay top dollar, she gave a Tony-winning performance that when I saw it at least was glamorous, well-sung and warm (much better than the awful Tony performance itself), she had very good attendance. At the end of the day, she seemed to do what was asked of her (cf. nightmare cases like Sheridan Smith in Funny Girl). At least if some of the factors hold true again, I'm not sure why a Producer would run away at the chance to have her again except that if she can only commit for this short amount of time it's probably difficult to recoup costs (this was rumoured to be the reason why other A-listers approached did not move forward with the production...Kate Winslet at one point or Cate Blanchett? I can't remember).
Give me claws and a hunch, just away from this bunch.