Thresh cant proc relic shield properly

Im not sure if anyone else has noticed but when thresh has the relic shield it wont properly execute the minions. example the minion is at 200 hp and the relic shield says it will execute a minion at 250 hp and below and nothing will happen when Thresh autos the minion. the charges will still activate when Thresh kills the minion but its not executing like it should be. Is this a bug or is it because Thresh is classified as a ranged champ.