Hello,
i have a problem with 5 Items (Worldquestitems) that are not going away in my List. Tryt to turn on completionist mode for 1 Minute and turn it off again. Shift clicked few times, nothing.

i have create a imgur album with 6 pictures and wirte down the Item Ids for the Items.

Album: https://imgur.com/a/PxUf1vD

It is because the other items are race locked, typically behind quests. Some quests will auto unlock it's opposite faction shared if the item is a quest item too.

Since they are for the opposite faction you won't have them checked off because you are unable to use those specific items for transmog. Judging by the items I am going to assume you are Horde. When you log on an Alliance character they would see the items correctly checked off.

Contrib Note: Discussed in discord I believe and figured out the issue.