Execute Effect of Relic / Targon's / Face of the Mountain not working on Thresh

Hi,

I have played two games with Thresh recently where I bought Relic Shield. It should do the following: "Melee basic attacks execute minions below 200 Health." In both games this did not work. I had to last hit the minions like if I didn't had a Relic Shield. If I did that, the other effect (Killing a minion heals the owner and the nearest allied champion for 40 Health and grants them kill Gold) did work however.

Also the execute effect still did not work, after upgrading to Targon's Brace and Face of the Mountain. This seems to be only the case with Thresh, since on other Championjs the execute did work fine.