Lots of blocks not rendering when under lava. It should be easy to see when moving around.

Only seems to happen with Sodium.

as felix said, this has to do with how sodium tries to avoid rendering chunks that are hidden by fog; there's not much I can do about it without some invasive mixins. Best way to avoid this is to disable fog occlusion entirely.

Only seems to happen with Sodium

You should disable fog occlusion in the Sodium video settings.