@ZimM: SpriteSharp currently isn't playing nice with the Unity Package Manager. When loading a project for the first time with packages being included, your texture pre-processor is trying to modify and re-import assets that are in packages. These assets are read-only and can't be modified so Unity enters an infinite loop and continues trying to reload the asset in a loop. We fixed this on one of our own texture pre-processors by adding a check that the path contained "Assets" at the start. Also, the sprite atlas hack changes the userData field but it would be nice if it didn't stomp what was already in there as we use it for something else.