I noticed this a while back. I didn't what was causing it then, but I think I have it figured out. Unfortunately, I don't know how to fix it.
The issue is where a Boss Challenge reward has an apostrophe in it. The template for the Item Page recognises that the item is a BQ reward, causing the line "As a reward for completing the following Boss Challenges:" to appear on the page, but the name of the BQ(s) isn't auto-populating.
For example: A Merry Party shows Rare Shyster's Sign as a reward, but if you click through the the seal page, the name of the BQ isn't there. Same thing for alternate version of the BQ A War Party and the Rare Pirate's Seal. This affects a lot of seals, but also Champion's Purse, which I found on the Category:Boss Challenge Rewards (it's the first place reward in The War of Five Kings).
If you check the Special:WhatLinksHere on the item page, it shows the BQ as a transcluded link; and the affected rewards are correctly being autocatted as Boss Challenge Rewards and appearing on that list.
I haven't checked the entire list of BQ rewards, but it's happened to a whole bunch of seals and I have checked Champion's Purse, Courtier's Outfit, and Champion's Greathelm. So I'm fairly confident that it's the apostrophe that's causing the problems.
Am I making any sense at all? Can anyone help me out here?