Nevermind, seems that this is fixed as of 2019.2.0b4. It appears that Image's mesh (e.g. shape, vertex colors) doesn't get updated when the used sprite is taken from a sprite atlas. The problem happens this way in my case: Inside a FixedUpdate, I'm changing UI Image's RectTransform's SizeDelta, Sprite and Color under certain conditions. The values do indeed get updated (according to Inspector), but the mesh doesn't. Changing the Sprite will keep texturing the old mesh, leading to some sprites having incorrect dimensions (e.g. mapping a 24x8 sprite, but the mesh is still same as the 8x8 sprite's) or having incorrect color. After I tried using only sprites that aren't defined inside sprite atlases, it started working correctly.