Error while running event subterra::on_chunk_generated (ID 12)
Unknown tile name: sub-dirt
stack traceback:
...terra__/scripts/events/generation/on_chunk_generated.lua:69: in function <...terra__/scripts/events/generation/on_chunk_generated.lua:14>
stack traceback:
[C]: in function 'set_tiles'
...terra__/scripts/events/generation/on_chunk_generated.lua:69: in function <...terra__/scripts/events/generation/on_chunk_generated.lua:14>

Well, I got the same issue after being in a world for more than a few seconds. I managed to fix it by deactivating Alien Biomes, which I used in my world. That also removed all the terrain and replaced it with the standard grass one. So I reverted back to an older save.
TL;DR: try disabling any mods which might affect terrain generation (RSO should be fine though)