After reading 

I figured Life Tap is bugged. Any plans on a fix soon? :( Can't get it to work 
(I think it's bugged, I've checked the options for it like thrice now)

Yup, I cant get it to work on Vanilla either. It WILL use Life Tap on "occasion" but when it does it only does it once. I even removed the use of all spells but Shadowbolt and Life Tap. Mostly, he will just sit there in melee attack waiting for mana to regen back to shadowbolts mana condition. Instead of Life Tapping back to Shadowbolts mana condition. Rarely, he will atleast Life Tap ONCE the moment he drops below mana threshold. Guess broken conditions is all we have on the private server side of things :(

 

EDIT: Fixed. I had to make Check if spell good distance "False" And Check if target is in view "False". Then it started working.