PBRMaterial (and NodeMaterial) refractions are incorrect if scene is using right handed coordinate system.
Playground example: Babylon.js Playground
See how the background doesn’t line up with the rendered refraction even with near 1.0 IOR. Left handed coordinate system works correctly.
Here is a test case for NodeMaterial: Babylon.js Playground
Looks like that one only happens when environment texture matrix has been rotated.
This PR will fix the problem: