Texture compression artifacts on Galaxy S6 only

Since upgrading to Unity 5, our texture quality has dropped significantly on the Galaxy S6 and S6 edge.

Our textures are split into color and alpha, both compressed using ETC1.

On all other devices this looks fine, and on the live version of our game, built with Unity 4, it looks fine, but on the Unity 5 version with an S6 there's some very visible artifacts.


The top image is from a Galaxy S5, the bottom is from an S6. They're both running the same version of the game, built with Unity 5.2.1p4.

Any ideas?