Smaller Viewports are getting grey images

When using smaller viewports like mobile it doesn't work and gets a grey image during reference and test, it's quite bizarre and happens for some components on the styleguide but not others.

```
{
name: "small",
width: 320,
height: 480
},
{
name: "small-medium",
width: 600,
height: 960
},
```
these are the viewports being used, and here is a reference image.