There was a little hidden bug, when sorting your inventory. >.>
Unequipping an item and then sorting your inventory right after would lead to that item to disappear. That should not happen anymore. ^^'
Bug Fix - Inventory sorting
Source: Steam Community (opens in a new tab)
Build and release context
Recorded Steam release date:
Within one calendar day of this post (UTC). The listed date does not establish an exact launch time.