[MC-131863] World generator problem

I've converted world from 1.12.2 to 1.13-pre3, and teleported to 0 64 0 (I've never been on these cords), and I see this:

Linked issues

Was it a superflat world originally? Can you provide the seed?

Patryk Matusiak 2018-06-22T19:22:26Z

It was Tunnelers’ Dream with stone lvl changed to 52

[Mod] violine1101 2018-06-30T11:09:24Z

Confirmed in 1.13-pre3. I'm unable to reproduce in 1.13-pre5 because of MC-132375.

[Mod] violine1101 2018-07-16T16:16:30Z

I'm not able to reproduce anymore in 1.13-pre9.