Why Is My Power Apps Canvas App Screen Not Centered After Publishing?

Question

I’ve built a Canvas App using Power Apps and designed the screen layout carefully in the editor. Everything looks perfectly centered when I'm working in the app editor.

But when I publish and run the app (especially on desktop browsers), the screen appears shifted to one side and doesn’t stay centered like it did in the editor, as shown below:

I haven’t made any changes to positioning settings that would cause this. What could be causing the app screen to not stay centered after publishing, and how can I fix it?