I’ve seen a short flickering of the system font before your chosen font had loaded. It seems like there are a lot of fonts loading (93% of your homepage size and requests are fonts).
WebFont.load({ google: { families: ["Nunito:200italic,300,300italic,regular,italic,600,600italic,700,700italic,800,800italic,900,900italic","Fira Sans:100,100italic,200,200italic,300,300italic,regular,italic,500,500italic,600,600italic,700,700italic,800,800italic,900,900italic","Poppins:100,100italic,200,200italic,300,300italic,regular,italic,500,500italic,600,600italic,700,700italic,800,800italic,900,900italic","Source Sans Pro:200,200italic,300,300italic,regular,italic,600,600italic,700,700italic,900,900italic","Nunito:200,200italic,300,300italic,regular,italic,600,600italic,700,700italic,800,800italic,900,900italic","Space Mono:regular,italic,700,700italic","Alfa Slab One:regular","DM Sans:regular,italic,500,500italic,700,700italic","DM Serif Display:regular,italic","Quattrocento:regular,700","Fanwood Text:regular,italic"]
Maybe you should try to get rid of the unused fonts first.
I don’t know about the minify options though.