For any activity, lift bounds start showing up for a given experience when it has reached the state of statistical significance in terms of confidence with respect to control and the confidence interval value.
What differs auto-allocation based activities is that there is no notion of control experience and the statistical significance of each experience is bound to that of the activity itself, which is attained when the true winner of the activity has been determined by the algorithm. Once that happens, lift bounds along with the other statistics - confidence and confidence interval , show up in the report.
Please refer Auto-Allocate documentation for more information around the same.