Reproduction steps:
1) Download and open attached project
2) Build and run "ShadowTest.unity" scene
3) Play game for ~10 seconds
-- Notice that shadows distort and flicker the further object from 0, 0, 0 position is

Note:
Reproduces with OpenGL and Vulkan (Metal on iOS)
Also, if position resets to 0, 0, 0 - shadows are rendered as normal (until object moves away)

Regression appeared in
5.6.0b2

Reproduced with:
2017.2.0b2, 2017.1.0f3, 5.6.2p2, 5.6.0f1, 5.6.0b2
Unable to reproduce with:
5.5.4p1, 5.6.0b1

Devices under test:
Reproduced:
Motorola Moto G4, Android 6.0.1, GPU: Adreno 405
Samsung Galaxy S7, Android 7.0, GPU: Adreno 530
Xiaomi MI Note Pro, Android 7.0, GPU: Adreno 430
Google Nexus 5x, Android 7.1.2, GPU: Adreno 418
Huawei Eva L19, Android 7.0, GPU: Mali-T880
iPhone 5s (iOS 9.3.3)
iPhone 6+ (iOS 8.0)

Unable to reproduce:
Nvidia Shield Tablet, Android 6.0.1, GPU: Nvidia Tegra
Sony Xperia Z, Android 5.1.1, GPU: Adreno 320 - no repro
Google Galaxy Nexus, Android 4.3, GPU: PowerVR SGX 540