Elder guardians doesn't give the player "Monster Hunter" advancement

this is a weird glitch. I don't know if this bug is in 1.12.1 or even earlier, but I just discovered this bug today. If I killed an elder guardian and I don't get the "Monster Hunter" advancement, it won't give me the advancement. That photo below is captured today. I don't get the advancement early. And same when I killed the elder guardian. Please fix it!