Very closely relates to MC-118561, MC-249040 and MC-249042 due to these concerning translucency. Partially blocked by MC-156980 (and to a lesser extent by something I described in the comments of MC-4), necessitating some weirder reproduction steps than usual.

The bug

Experience orbs do not render inside of a boat.

How to reproduce

1. Build a 3x3x3 glass cube with a repeating command block at the bottom and a top-half slab in the center
2. Set the following command in the repeating command block: tp @e[type=minecraft:experience_orb] ~ ~0.5 ~
3. Use a command to place a boat inside of the cube by standing on top of the center of it and running /summon boat ~ ~-2 ~
4. Activate the repeating command block and throw bottles o' enchanting
5. Use Spectator mode to try and look at the experience orbs

Expected results

The experience orbs would be visible inside the boat.

Actual results

From outside the boat, they are not. Only when the player is also inside of the boat are they visible.