Samsung Galaxy Tab S5E Performance issues with Vulkan

[nex86]

Yesterday I got the recently released Galaxy Tab S5E and tried the latest svn of Dolphin.
The framerate in Twilight Princess or Windwaker (GC version) fluctuates a lot when using Vulkan.
like it jumps from 30fps to 11fps back and forth.
I get a more constant framerate using OpenGL. its about 20-30fps.
Still getting framedrops in certain situations but not as bad as with Vulkan.

Shouldn't it be the other way around that Vulkan performs better?

The Tablet sports a Snapdragon 670 with an Adreno 615 GPU.

[Helios]

Vulkan doesn't always perform better, especially on mobile where GPU drivers are generally buggy pieces of shit