Terrain flatten not flattening correctly

Video:

System Information:
CPU: 13th Gen Intel i7-13700KF
RAM: 64GB
GPU: NVIDIA GeForce RTX 2060

Beta Features:
I have all beta features enabled.

Problem
The problem I’m having is the flatten tool is simply not doing what it is meant to do and what it used to do - it isn’t aligning with the actual terrain that I first start on and is subtracting terrain and flattening to a different level than what it is meant to. I understand that I could use a fixed flatten plane but that just feels counter productive to what the auto plane tool is meant to be used for. I have seen others report the issue on the Dev Forum but so far nothing has come of it and has been left unnoticed by Roblox staff.