Versions

• Minecraft Version: 1.16.4
• Forge Version: 35.1.37
• Mod Version: "Waystones 1.16.x v7.3.1"
• Do you use Sponge, OptiFine or Vivecraft (and which?): Optifine HD U G7

Describe the bug
In a world created with MC 1.12.2 and Waystones 4.1.0, converting the world to MC 1.16.4 with the versions mentioned above caused all waystones auto-generated in villages to vanish. The surrounding structure remained intact, but the actual waystone was gone. The waystones list in the warp stone UI is empty after conversion.

I also observed a strange failure mode with a world that was originally created with an even older MC version. Here, all waystones were converted into two observer blocks stacked on top of each other. Not really sure what's going on there.

(I'm aware of #259, but as far as I understand, waystones not being generated in new villages shouldn't cause already existing ones to disappear.)

To Reproduce
Steps to reproduce the behavior:

1. Create world with MC 1.12.2 and Waystones 4.1.0, ensure that waystone generation in villages is turned on
2. Look for any village with a waystone
3. You can activate it or not, doesn't make a difference
4. Switch to MC 1.16.4 with versions as mentioned
5. Waystone is gone

Expected behavior
Waystones should not be deleted from the world (and they shouldn't turn into observers either …)

Upgrading worlds between major Minecraft version differences is not always supported, as was the case between 1.12 and 1.16.