Want to start off with saying that what I am seeing is different than chunk borders caused by making infinite, this is a type of world corruption, vs just standard chunk borders.

Old worlds that are converted to infinite end up with already generated chunks force-regenerating. 

Steps to reproduce:

1.  Create a new old-world-type world in a version that supports it.
2.  Explore it completely.
3.  Save and exit the world.
4.  Go to world settings and click/tap "Make Infinite!"
5.  Enter the now infinite world.
6.  Some already generated chunks have now been regenerated with new chunks, causing chunk borders where there shouldn't be.

I am able to repeatedly reproduce this, on multiple different seeds and even on multiple devices.

Attached are screenshots of one of the worlds I tested this on. One of the screenshots has the regions where chunks borders are expected shown in green, and the chunk borders which shouldn't be there in red.

I feel this is important to bring up since people might want to switch to infinite from old now that old worlds are being phased out (1.18). And if they do it might be challenging to do so without it bugging out.

Again would like to clarify that this bug is separate from the intended chunk borders that occur after making a world infinite.