I've started doing hard clues again and have noticed that the passive with the shorts for the double agent spawn never works. I also can't find anything talking about that passive anywhere, but that passive still works with master clues. I'm not sure if that passive was unintended for hard clues just curious! (passive being a chance for the double agent to not spawn)
I have never heard of the shorts having a passive effect.
As far as the double agent not spawning, even when wearing the shorts, it seems to follow the condition mentioned in the wiki,
https://runescape.wiki/w/Double_agent
:
"If the player's clue scroll starts off with an emote clue, the double agent will not appear. This may be a glitch, as every other emote clue will cause a double agent to spawn."