After going from Thorns Keep to the Storm Horn Mountains I wanted to use my helmet of armour (The one received from Kit in Haven) when to my great horror I saw it had disappeared from my inventory. I searched all my bags and inventory, but no helmet. I had just buffed in Thorns keep so I stepped back and searched the ground - no helmet. Then I reopened my inventory and the helmet had reappeared next to my other helmet.
I then relogged and this time the helmet appeared in my inventory as it should.
I know the obvious answer is that I had overlooked it the first time, but I am certain I didn’t. It is placed next to my standard helmet in my inventory and that space was empty. I have experienced invisible items before (they don’t appear, but they take up the inventory space, nothing can be placed there), but since this concerns an important item I wish to report it in case it reoccurs.