Don't know if this helps but I have noticed that tridents that have been thrown by drowned will make the pick-up sound and disappear but do not show up in your inventory. However, if you kill a drowned and the trident appears as a floating icon it is pick-upable.
Joshua Foley
Don't know if this helps but I have noticed that tridents that have been thrown by drowned will make the pick-up sound and disappear but do not show up in your inventory. However, if you kill a drowned and the trident appears as a floating icon it is pick-upable.