My breakpoint is 480px:
Problem #1: the Heading element does not align horizontally to the center although I set it to align center at 480px.

This is my settings for the heading:

Problem #2: the Layout Grid loses its settings at 480px. I have set the Shape element align to the center by chosing center alignment for the column but keeps aligning back to the right of the column

This is my setting for the Layout Grid:

I have tested this in Firefox, Opera and Chrome. Same issues in all browser.
I have the file here for you to look at.
https://filebin.net/82g6zssx2kkf6hl5