Bumpy shadow edges in both the Unity editor, and on Android

I've been trying to work out what's wrong with my shadows for a while now, but I'm getting nowhere so far, so hopefully somebody on here can help out!

The edges of the shadows in my scene are appearing bumpy, even though the surface that's projecting them is perfectly smooth. I've tried changing various shadow, lighting, and project quality settings and nothing seems to be helping so far. I've attached a link to a couple of screenshots below. Any help would be greatly appreciated!

Screenshots Link