5.6.0f3 black flashing triangles on some devices

Our game is flashing black triangles on some textures and the skybox. This only happens on some (older) Android devices.

The outline of these black triangles do not correspond with the shape of any of the textures or any polygon. They go across multiple textures chopping off parts of textures, but don't match with any in particular.



The skybox also flashes with black and white streaks.


We have built with all the different combinations of build settings, but to no avail.

This is happening on the Samsung Galaxy Tab 4 and Kindle, but not on Huawei P8. The same happens with Unity 2017.

Does anyone have any idea what kind of issue this is?

TIA