Any idea what could be causing this?
I used this item to gain appearance on a paladin, should be tagged "collected"?
this is happening to quite a lot of different plate items

thx

Thank you! Shift clicking refreshed it and now everything shows as collected :) strange.. ive wasted a few of duplicate expensive transmog pieces on this without realizing xD

Yea, maybe try re-logging if you notice this happen in the future as it might fix whatever happened on Blizzard's side to stop sending the events to your game Client about learning new appearances.

You can also try using 'Can I Mog It?' in addition to ATT which will basically force-query for everything which generates a tooltip and tend to be accurate in situations such as this. Whereas ATT relies on a lot of 'cached' information to prevent unnecessary processing lag in-game, but this means that unexpected behavior from the game itself can lead to unexpected behavior in the addon.

When you Shift-click an ATT window to force refresh everything, do they still show as Not Collected?

I've noticed that with some other items recently that WoW does not fire any events that you've learned a new appearance, thus ATT never notices or performs any logic concerning the items.