Lunar Convocation’s first ability cares whether you gained life this turn, not how your life total changed. For example, if you gained 2 life and lost 1 life in the same turn, you still lost life. You also still gained life, which is relevant for Lunar Convocation’s second ability.

If you haven’t gained life during the turn when your end step begins, Lunar Convocation’s first ability won’t trigger at all. Gaining life during your end step won’t cause the ability to trigger.

Similarly, if you haven’t both gained and lost life during the turn when your end step begins, Lunar Convocation’s second ability won’t trigger at all. Gaining and/or losing life during your end step won’t cause the ability to trigger.