Hello,
As per the docs, the WebGL2 shadows are meant to fall back to Poisson Sampling on non compatible devices.
However, Chrome 65.0.3325.109 on Android (Samsung S6 edge+) only display a red cube on this PG without ground and no shadows.
That said, Chrome >= v. 64 should support WebGL2. and checking on another Android phone, with Chrome 64 it shows shadows.
Is this a bug?