Icons are distorted in Mobile and Tablet view

I'm in Robohelp 2017. I'm using corporate-approved icons, so I can't swap them out for other images. I'm editing the Charcoal Gray layout, and the icons look fine in Desktop view. I saved the same icon as every view, in both active and passive, so it's exactly the same icon throughout. However, when I display the same icons in Tablet or Mobile view, they stretch horizontally. The most noticeable ones are the Index and Glossary icons.

I tried editing the image size so it was stretched vertically to counteract the distortion. A also tried adjusting the canvas size and the image size in Photoshop. However, the icons still look exactly the same.

Desktop Icons

Tablet Icons