I and other paladins I raid with noticed a substantial drop in DPS over the last 2 days, I have also noticed (or atleast I think I did) that my judgement hits were not always showing up in SCT though I didn't think anything of it till I read the most recent posts here. If this is true it would explain alot of what I have been experiencing. Naxx was surprisingly lag free when I experienced this and my frame rates are solid so I can only assume that some sort of ability clash seems likely, either with master poisoner as suggested or perhaps with other ret paladins in the raid, of those of you who have experienced this were you raiding with another ret pally/a rogue with master poisoner?
most likely blizzard didn't think things through. what's probably happening is that judges are not overriding other judgements. and since Vengeance seems to affect judgement (+% holy dmg). so instead of getting "there's a more powerful spell..."-error. it simply doesn't apply.
this would explain why sometimes it does show for you (you have a higher Vengeance stack; so your judgement is more powerful).
most likely the culprit is in the WG-hotfix that was done : /