MC 1.17.1
Fabric loader 0.12.4; API 0.41.3
Chalk 1.0.1

To reproduce:

1. Create a world with extended height (using an official 1.18 preview datapack for example; I use this one, which includes the official datapack)
2. Go below Y0 and try to draw an arrow pointing upwards

Examples:

Y0, pointing at the top center of a block:

Y-1, pointing at the top center of a block:

Y0, pointing at the upper left corner of a block:

Y-1, pointing at the upper left corner of a block:

This should be an easy fix. Ty for the bug report!

Fixed in 1.0.2 via 0b7579d