UI not batching sprites with same material.

In the image you can see 4 sprites placed in the canvas which are ordered next to each other. Everything in the 4 sprites is the same in the Frame Debugger. I tried with static/dynamic batching, the Z index is the same, the sprite atlas is the same, the settings of the images are the same. I have other elements that are batched correctly so the batching work. But i can't figure out what is the issue with 6 - 7 UI images that are just not batching. The bellow image shows 4 of them .