What happened

When I use a modded block (currently using chisel mod to make basalt with meta 4 replace cobblestone) in the tab, export that to the .dat file, and generate a world, it works fine. When I then relaunch minecraft and make a new world, the modded block is swapped with minecraft:air. The .dat file still shows that it is supposed to swap cobblestone with chisel:basalt1@4

Used versions

Minecraft-1.12.2
VerticallyStackedDimensions-0.1.9
CD4017BE_lib-6.5.1
Forge-14.23.5.2854