FYI, I just found out that The per page Masonry option is broken in version 3.1.1
May be not your issue as you have some pages that work, but just to let you know as not to confuse things any further. If you are using 3.1.1 then that is likely the issue.
Are you using 3.1 or 3.1.1?
Did you try creating a test page with the script in the page content as I asked (in Text mode with “Allow Raw HTML and script” checked) , and if so does the script work there?
Not a JavaScript expert, but I don’t see any glaring issue with the script