Relic Shield and Targon's Brace doesn't proc properly on thresh [GAMEPLAY]

at first i didn't think anything of it, but is anyone else having issues with the relic shield and targon's brace passive not proving properly on thresh? i can use any other support champ and make it proc when the minions are half health. but when i use thresh it doesn't work like it should. and its making it really annoying to support properly due to me stealing cs. It chooses when it proc and when it doesn't. RIOT please look into this. it doesn't seem right.