At the start of the battle, the Karazhan chess pieces target the choral murloc, and that’s it—the choral murloc’s effect didn’t activate, and I lost a free game because of it."
Had something similar happen to me just a minute ago. I had one choral and Karazhan chess pieces trinket and it worked fine, the minion was duplicated and buffed. But later I bought a second Choral and boom, only duplication but no buff happened.