What browser are you using? The site seems to be responsive in Chrome (1440 width shows four columns, 1920 shows five, not sure where the breakpoints are exactly).

EDIT: It's using a flexbox grid layout so it shouldn't actually need any breakpoints. Maybe the layout changed since you checked it or your browser is triggering a fallback?

I have five columns on my 1920x1080 screen using Firefox, dont know if that makes a difference.