Improperly-rendering chunk borders

For some reason, on my Fabric 1.21.4, the chunk borders are broken. You may have seen this image in my very first bug report about the block lighting issues:

<img width="1920" height="1080" alt="Image" src="https://github.com/user-attachments/assets/cf9b39de-8672-4492-876c-7b7d0ec635b1" />