Hey guys, we’re working to track this down; it’s an issue with the pow() function when calculating fog; can you try modifying the fog component in your map? Alternatively you can modify BasePassForForwardShadingCommon.usf locally and change #define USE_VERTEX_FOG to 0 (but this will remove all fog).
We’re still trying to get a good workaround! The one suggested by Apple has perf implications 