Sprite editor automatic slicing not working

I'm trying to use the automatic slice in the sprite editor to slice a sprite sheet, however when I press the slice button nothing happens.

I've got sprite mode set to multiple, the background is transparent in my .png file, so I'm at a complete loss for what the issue could be.

Anyone have any ideas?

Here's a screencap of the inspector and sprite editor: https://i.imgur.com/Q3vMzHs.png