Terrain issue? Any idea?

https://gyazo.com/0252c4144a1e95556497cb60071f39bd

How come this happens? Or is this a studio bug?
Tons of terrain gets deleted when I resize

The Region tools act a bit differently than the similar part tools. Maybe the pic below will help? I’m unsure from your video if you had a region selected before you resized it. Sorry if this doesn’t address your issue.

Screenshot_20220826-213640_Chrome