I didnt have this issue yesterday but I bought two new unique items.
Chest : something Pride
Belt: Viper belt.
Both dissapeared when I left the game and re entered although, for the belt it was replaced with a rare item? I was crafting at the time (my amulet) and it fractured so I wasnt sure if it affected the belt in some way?. Should not of from the crafting I have read , but only explanation I could come up with for why the unique viper belt became a rare.
The chest piece, I bought from a vendor, then I exited back to character menu. Came back in and no chest piece was on my character.