Argent Diffender Title

Hello, my 9 mates had an issue regarding the achievement. We cleared 2 runs in 2 days, but no achievement was given. We checked each other before starting, ensuring everything was clear: no tabards, no shirts, all gear is legit. But somehow we didn't get the achievement (ofc we cleared without a wipe)

After checking the stream, we realised Paladin had left buff from his Tiny Jar trinket (4 stacks of Motor of Anger), and we think that because of that, we didn't get the achievement, but yesterday we checked again each otehrs gear and in fact we removed all literary all kind of buffs and entered TOC after that. But still NO ACHIEV! We don't know what was the reason the only thing we think is that Retri Paladin had weapon transpog for the run, could it somehow bug the achievement like tabard or shiert does? any cases like this guys?

The easiest solution is: Someone did a mistake with his gear.
Maybe swapped something using a macro or anything along those lines? Which gear are you actually using?

A bug is of course always possible. But you should rule out human error first entirely.