Something similar happened to me but instead of being void it resets all of my chunks all my builds and stuff are gone here is the world link
is.gd/QYKc6w
The zip includes the backup and the world in which it happend
Here are the steps to reproduce maybe I don't have access to older versions
It includes nether portals
Steps to reproduce
1. create a world in older version than 1.17
2.Enter a nether portal
3.open the world in 1.17
4.Go back to the overworld
And all the chunks are resetted
By looking at inventory you can see ehat sre from the backup
ItzUG
Something similar happened to me but instead of being void it resets all of my chunks all my builds and stuff are gone here is the world link
is.gd/QYKc6w
The zip includes the backup and the world in which it happend
Here are the steps to reproduce maybe I don't have access to older versions
It includes nether portals
Steps to reproduce
1. create a world in older version than 1.17
2.Enter a nether portal
3.open the world in 1.17
4.Go back to the overworld
And all the chunks are resetted