NOTE: I may have submitted this earlier in another area.
When I first received the Pink Party Hat from a Guildee, I was with the Kyrian Covenant and learned the Pink Party Hat for the tramsmog. I am now currently with the Venthy Covenant and working on the Achievement “Rendle’s Big Day”. I have the other three hats done but the “Pink Party Hat”. The Pink Party Hat is in my bag and it shows that it is “Already Known”. I am now in front of Rendle and Cudgelface in Sinfall and Rendle does not have a quest for me. I have tried to turn it in when the Ember Court party is active and he is there.