Calling Texture2D.Compress(bool), then Sprite.Create() creates a sprite with a blank texture. This is due to the fact that Sprites can only be compressed with width/height multiple of 4 and with mip-map off. However, the error messages that get printed in the console have nothing to do with the problem, and left me clueless as to how to resolve the issue.
Please print an error that at least mentions the multiple of 4 / mip-map requirement.

1. Open scene "scene4".
2. You should get error messages:
"GetPixels32 failed: insufficent pixel buffer size (29056), must be at least 228 x 128
UnityEngine.Sprite:Create(Texture2D, Rect, Vector2)
UIHeroImage:SetUpSmallImage(Texture2D) (at Assets/UIHeroImage.cs:18)
UIHeroImage:Start() (at Assets/UIHeroImage.cs:11)"
...