As the title says, dirt in the Primordial Caves won't turn to grass unless there is a light source like torches near it. I assume it is because of the actual light level of the Primordial Caves in the f3 screen being 0. Exactly the problem shaders have with the said cave. This problem causes random ugly dirt patches in the Primordial Cave specially after the eruption with the boss messing with the grass with magma and stuff. I hope it will get fixed. Examples are seen in screenshots below.