[GAMEPLAY ISSUE] Thresh & Relic Shield Bug Perhaps?

So I tried out thresh for the first time 2 days ago, and I got relic shield like I normally do for my tank supports, and every time I tried to execute a minion it wasn't executing it. I even would check the health needed to execute along with the minions health and it still wasn't going. It would give the gold to myself & the person nearby if I landed the killing blow like you would do when just regularly CSing. (I even had charges for the executes) Thought I was doing it wrong until yesterday when I was playing Poppy and the Thresh support we had was freaking out about the relic shield not working. Which I realized it might not have just been me. I played Leona in another game, and the executes were working perfectly fine. Just with Thresh it wasn't. Haven't tried any other supports than those two. (I lied, I did Blitz and he was fine too)