Dropped items do not render behind transparent blocks. This is not the case for dropped blocks (such as stone for example), however transparent blocks are affected as well (see MC-165156).
Food items and slime and honey blocks can not be seen under water
Items with no 3D model are invisible through the water's surface
Flat items no longer render behind transparent textures
Items Do Not Render Behind Glass, And Sometimes Water
Items do not render in water
item and breaking invisible under water
The new snapshot 19w46b has a new bug on items under water.
Campfire-cooked items appear invisible in water
Visual Underwater Bug
Seeing Blocks Through Water in Newest Snapshots is bugged.
Shulker boxes do not render behind transparent blocks
Filled item frames do not show the item when viewed through glass
Under certain circumstances mob body parts don't render underwater
Transparent block items no longer render behind transparent blocks
Banners are rendered completely white when looking at them through transparent blocks
Items held by entities don't render through transparent blocks
Items do not render behind transparent blocks while being picked up