I had voxel mode enabled on higher priority than heightmap. I am running this in Custom Cubic type world with Optifine 1.12.2.

Not only the mode does not work (no extra terrain is drawn), it also prevents heightmap based terrain from displaying.

When I change to heightmap only mode, LODs are drawn over normal terrain. Although there are some chunks which mod has no trouble displaying.

LOD is set to 22, cutoff is 256, render distance is 9

Modlist:
[MixinCompat-1.1-1.12.2]
CubicChunks-1.12.2-0.0.1271.0-SNAPSHOT-all
CubicWorldGen-1.12.2-0.0.152.0-SNAPSHOT-all
ForgeRocks-7.7.3-1.12.2-full
fp2-0.0.1.617-1.12.2