I’ve been working on this one all day; tried it on vet, champ, and legendary difficulties all in some combination of specials, books, and monster setup so I can make sure I actually do complete the second duty listed right after the first while playing the grail knight. I know I got this done within 5 seconds several times and it won’t unlock. Playing on xbox
So I figured it out; I had to select the Virtue of Purity talent for it to register. I had Virtue of the Penitent on for every other attempt. As soon as I switched talents, the challenge popped the very next try. Not sure if that’s working as intended, but that’s what did it if anyone else is having this issue.