Isotope.js with rogue margin on masonry layout

Hello,

I have made the masonry grid gallery layout using Isotope and Vanilla JS. Everything seems to work fine, but on resizing there is some kind of the right margin on the masonry element, which is getting bigger as the viewport size gets smaller.

Everything would be fine but there is no mention of any kind of margin or padding or anything in Chrome dev tools.

Here is the link to the codepen with the code: Masonry Grid

Please help, I am slowly going crazy :)

THX

JR