Left is on studio, right is in game. The green gui on the left is centered in the middle of the screen (0.5, 0.5) and sized to go to the bottom. The mouse on the left is clearly offset from the center a big amount, but on the right is only offset from the center by a slight amount. A gif to show the right side offset better.
Found out the mouse jumps down when it’s unlocked with a gui on the next mouse movement. Gif to show this. I’d zoom in which triggers a mouse lock, open the inventory which prompts an unlock, and when I move my mouse after unlocking it causes the mouse to jump down.
Repro steps are pretty simple, mark off the center of the screen with a gui, test in play solo, start server, and in game. Repro place used in the images. jababbabba - Roblox
For reference this was tested for on a Window 10 PC.