All the linear gradients ar not well replaced. Previous mixin was doing following thing:
linear_gradient($background_color, $gradient_color, $gradient_color) = fallback color + gradient consisted from 2 colors

current implementation does:
linear-gradient($gradient_color, $gradient_color, $gradient_color) = gradient consisted of 3 colors

That's why in the example the primary button consists of the gradient of 3 colors.