The resource pack attached offers a complete fix for this issue. Mojang have my full permission to (and are encouraged to) replace the affected vanilla model files with the contents of the resource pack.

Download resource pack:

• 21w41a: beacon-fix-21w41a-v1.0.zip

The bug

The beacon model contains a face which cannot be seen without clipping into the beacon block itself. In addition, seven of the beacon's faces can be fully occluded by blocks. For most models the cullface feature is used for obscured faces like these, however they are completely absent for the beacon, which is inconsistent and wastes resources on rendering these faces.

How to reproduce

1. Place down a beacon
2. Enter Spectator mode
3. Position yourself inside the beacon such that you are inside the obsidian cuboid and can see the bottom of the blue cube
4. Now place opaque blocks around all six faces of the beacon, and enter each one of them

Expected results

As the bottom of the blue cube is never visible without actually clipping inside of the beacon model itself, it shouldn't be defined in the first place, as is the case with many other models with faces like these. In addition, the glass faces and bottom of the obsidian cuboid would be expected to be culled against opaque blocks due to never being visible in these cases without clipping inside of solid blocks.

Actual results

The bottom of the blue cube does in fact exist, and none of the seven obscurable faces are culled.

How to fix

As with many of my other reports in this vein, a resource pack is fixed which fixes this issue entirely. The beacon model currently in the game can quickly and cleanly be replaced with the model in the pack to eliminate this issue once and for all.

The formatting in the model has also been cleaned up to be consistent and more readable, and I also removed the line that disabled ambient occlusion as being a light-emitting block this ultimately changed nothing about the model.