[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:

Environment

System: Windows 10 Home

Processor: Intel Pentium 2020M 2 x 2.4 GHz

Graphics: Intel HD

RAM: 4 GB (usable 3,88 GB)

Mobo: Acer Aspire E1-731G

Java: Lanucher Runtime (Lanucher updated today)

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

It was Tunnelers’ Dream with stone lvl changed to 52

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

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