This screenshot is taken with a Xiaomi MI4 the same scene works nice on almost any smartphone but it looks weird in that one.
It projects a cubemap over geometry
And the effect gets increased when you zoom over the scene (changing the fov)
Thank you in advance for any tip!
This unfortunately looks like a precision issue on their side
you could try to change the camera.minZ to see if that changes anything ?
I tried that clipping change but I had no luck 
Are you relying on compressed texture ? or hdr textures ?
Just regular jpgs anyway it is not so important since it is an ancient device but you know making this working fair in any device is nice
Yes I totally aggree did you try :
- forcing webgl 1 (through the engine constructor options)
- forcing med precision : engine.getCaps().highPrecisionShaderSupported = false
forcing webgl 1 improves the the result a lot!
with engine.getCaps().highPrecisionShaderSupported = false it comes much worse
So probably a webgl2 driver issue you might need to disable webgl2 support for those devices 