I stored a Deus Specs on Dispenser 55 and put it on trade for 2 refined.
I come back to it a few weeks later, and it looks like no one traded for it, so I canceled it.
After I canceled it, the Deus Specs was available for me to retrieve it, but as I checked Dispenser 55's inventory, it wasn't there.
Although the trade could have been completed and Dispenser 55 now has 2 refined available, it doesn't say a trade has happened.

(EDIT: Oh, I'm an idiot, I didn't see the thread for missing items, sorry!)

It's weird as I do not find either your item or the metal (However the trade history suggested that your item has been bought.)
I added 2 credit to you so that you can withdraw metal from our ATM bots.

But for debug purpose may I ask if you have ever relocate your bot or closed your shop?