Why does mez sometimes seem to never blur a particular mob?
 

I never bother to spellswap mem blur (I don't think I even bought it), because mez is normally so effective at blurring. I hear that your charisma helps, and I have about 230 buffed so mez blurs way more than 50% of the time it feels like

But occasionally some mob will seem bugged to where it is just immune to blur from mez. I think I've attempted like 15 times in a row before just giving up and dealing with the mob in some other way, and this has happened on a few occasions

I am not standing in aggro distance, nor is anything socially aggro'ing it. I also haven't put any debuffs on it, although I have countless times been able to blur mobs after hitting them with wandering mind. It's a great way to get some mana on the go, just mez a nearby caster, then wandering mind it, then mez it again. You should get back more mana than you spent on the mez's. So I don't think having a debuff up should prevent mez from blurring, only a damaging dot should do that, but regardless, no debuffs up sometimes and mez still won't blur

Is the game RNG seed just getting stuck? Or am I just paying more attention to when I get really incredibly unlucky?

stand away from them

I also heard standing behind the mobs LOS helps with blur, haven’t personally corroborated that one though.

But also just buy mem blur…

you're too close to the mob

Could you or your pet have dotted the mezzed mob? Some enc debuffs have dot component.

Do you paci before memblurring? That would prevent it from re-aggroing if that is, in fact, the problem.

You say you’re not standing in aggro distance - are you sotting? Is your pet nearby?

Magic resist affects the chance of the mob blurring. Put tash + pacify on it first. Higher MR mobs are more difficult to blur.

What was the name of the mob in question?