When an item display entity and block hitbox overlap the line of the hitbox becomes transparent, this results in the blocks behind the item display being shown.

It looks like this only happens for item-like items, like diamond hoe or golden apple, for blocks like fences and stone blocks it does not happen, even if we use a resourcepack to modify these to an item-like model

To reproduce:

1. Place an item_display with an item as item(like a diamond_hoe) /summon minecraft:item_display ~ ~ ~ {item: {id:"minecraft:diamond_hoe",Count:1}

   ,}

1. Place some block behind it that has a colour that is easily distinguishable(like a command block)

1. Place a block that does has a hitbox that does not overlap with their model

1. Look at the item display through the hitbox of the block

In the attachments you can see the colour of the block behind the display being shown on the hitbox lines of the item display