The dirt mask is only supported with the filmic tonemapper, and the filmic tonemapper isn't supported on devices which don't have FP16 render targets. The devices listed all use the encoding emulation mode.
Updating those devices' firmware will add FP16 support which will allow filmic tonemapper and dirt mask.
In some mali devices (Galaxy S6, SC-05G, Android 5.0.2 / Galaxy Note 5, SM-N920C, Android 5.1.1) cannot display dirt mask in the bloom effect.
This is well displayed in iPhone 5s, LG G4, Nexus 5
1) Create a Postprocess volume in new project, Set Bloom intensity 8
2) Add one point light to see bloom effect
3) Add Dirt mask in the postprocess volume, set intensity 8
4) Play in device and move into postprocess volume to see the dirt mask is applied.
Expected: Dirt mask effect is visible.
Result: The effect is not visible in some mali deivces.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-37199 in the post.