[Experimental] Loading world (created before 1.17.20.23) creates a huge mountain at the exit site

Summary:

Loading the experimental world (created before 1.17.20.23) creates a huge mountain at the exit site.

Steps to reproduce:

1. Create a world with experimental gameplay in 1.17.30.22 (and below)
   or you can download my world. (not open at 1.17.30.23) MCPE-139669.mcworld
2. Enter the world at 1.17.30.23 (most likely you will spawn in a cave)

Observed results:

Loaded, the nearest area will be turned into a mountain.
And also the bedrock will be raised.

Expected results:

The generation of loaded chunks should not change.

Image: