Minecraft v1.16.5
Forge v36.2.4
Apotheosis v4.8.1

When the enchantment library is facing east/west, it produces an odd shadow on its side, which is more easily visible if multiple are placed together. It doesn't have this problem when facing north/south.

what in the world

¯\_(ツ)_/¯
Yeah, I've never seen something like this before either.
Forgot to mention this was on a server, but probably unrelated.

It would appear you have to set experimentalForgeLightPipelineEnabled = true in forge-client.toml to get the model to be shaded correctly.