Hi,
found weird bug with shadows.
Device: Galaxy S4
OS: Android 5.0.1
GPU: {vendor: "Qualcomm", renderer: "Adreno (TM) 320", version: "WebGL 1.0 (OpenGL ES 2.0 Chromium)"}
Browser: Chrome (62.0.3202.84) / Native (6.2.01.12)
Have mesh with PBRMetalnes material and ground with PBRMaterial.
Added spot light as shadow light and included sphere as caster and box as receiver.
Than created instance of the sphere. And after that both spheres disappear in S4 device.
Sphere dont disappear if instead of instance, clone is used.