Reilic item

If it's with , you most likely proc her W passive instead. Not sure if Riot has started looking into it, or is this intended.

If you mean why it doesn't execute minions at 200hp with , it's because the proc only works on melee champs, while Thresh is considered range, so which means you can only proc the relic stacks by last-hitting minions as an ordinary usual range champion. It looks as it seems he can execute the minions and grant relic stacks while minion has like a slack of HP, as observed in other Thresh games, only because of his E passive wind-up bonus damage.