The Bug:

The inside of a boat blocks the rendering of structure block annotations.

Steps to Reproduce:

• Summon a structure block with some annotations.

/setblock ~1 ~ ~ minecraft:structure_block[mode=save]{mode:"SAVE",name:"minecraft:test",posX:1,posY:0,posZ:1,powered:0b,showair:1b,showboundingbox:1b,sizeX:5,sizeY:5,sizeZ:5}

• Switch your graphics to "Fabulous!" if not already.
• Place a boat inside the structure block annotations.
• →  Notice how the inside of a boat blocks the rendering of structure block annotations.

Information:

This issue can also be seen whilst using the "Fast" or "Fancy" graphics settings, but only from certain angles.