On Mojave as well and just switched the scroll settings to “Always” — yup, that breaks it. Is this a common problem with with Masonry? Didn’t think to test that and not sure how to fix
Masonary style scripts are really hard to do. The math involved to figure it out and get good performance is just crazy. However, browsers have moved and you can get pretty much this effect now through css grid(like this https://codepen.io/balazs_sziklai/pen/mOwoLg) - theres plenty of other ways out there, google around. Im guessing that Mojave setting changes the width of the viewport in a different way, throwing out the maths and making it think there isnt room for another column.