During gameplay, especially in worlds with high tick processes (I found this to happen most often during long sessions in Amplified worlds), if the player gets caught on a lag spike, sometimes a deadzone generates in the top-right inventory slot, which causes said slot to be broken and barely interactive.  Items are extremely difficult to remove and insert into the slot, and it takes several clicks.  This issue is infrequent and depends purely on tick rate of the internal game process.  The game has to be closed and reopened in order to fix.