I’ve submitted a bug report in-game as best I could (we really need more characters to actually submit bugs with, tbh).
I found Trading Post Items Dissapeared as well, and the bug detailed in here with regards to some Trading Post items completely disappearing out of Collections sounds very similar. I don’t know if they’re correlated, given the Guardian items are not yet on the Trading Post, but are planned to be… but yeah.
If it isn’t related, though, or no one else posts about it, I’ll submit a formal bug report on the forum.
I’d appreciate if you could! This seems like such a weird bug to be hit with - especially so when the Cloak and Hood items didn’t disappear. I still see them in my Collections.
It’s just the Standard - which happens to be the only part I really use, and had actively transmogged at the time.