I appreciate text explanation, but video is required for me to be able to provide with specific actions.
In general I can suggest you to review elements size: are they in PX or in %
What dockings are you using for the elements got problems on?
Are grids setup correctly to have more control over the elements positioning?
If we are talking about the text, do you use scaling?
If site looks good only at 67% zoom out, this means that you are working on large screen resolution on Editor X most likely, so when you are doing the review on the live site version, zooming our is required to see the content properly. This could be caused by sections sizing, grid cells sizing, dockings, text scaling and so on.
In general this article could be useful for you:
https://www.editorx.com/shaping-design/article/how-to-make-a-responsive-website
but still without proper video explanation, I can give only general suggestions, like use text scaling, % for dockings, grids for element to have more control