I am using Subterranean Wilderness with it added to the Valhelsia 3 modpack. After noticing that all SubWild half blocks were missing their side textures, I isolated the mod that seemed to be causing the issue. No other mods or shaders are installed.

REPRODUCE:

• Create new instance in Curseforge launcher (Forge 36.0.35)
• Install Subterranean Wilderness (SubWild-1.16.5-1.1.2.jar)
• Install FerriteCore (ferritecore-2.0.1-forge)
• Create new world, find cave

Apparently this was an issue with FerriteCore and fixed by updating that mod to its latest version (ferritecore-2.0.3-forge)