To reproduce:
1. Open the attached project;
2. Make sure Procedural Skybox ("Skybox_mat") is set as Skybox Material in Lighting Settings;
3. Build and run the SampleScene on Android devices with Mali-400MP GPU.

Expected result: skybox is rendered correctly.
Actual result: the ground of the skybox is black.

Reproduces on: 2018.3.8f1, 2019.1.0b7, 2019.2.0a8.

Devices under testing:
Reproduced on:
VLNQA00110 Samsung Galaxy Note2 (GT-N7100), 4.4.2, GPU: Mali-400 MP
VLNQA00126 Samsung Galaxy S5 mini, 6.0.1, GPU: Mali-400 MP
VLNQA00048 Samsung Galaxy S3 (GT-I9300), 4.3, GPU: Mali-400 MP

Not reproduced on:
VLNQA00175, Samsung (SM-N960F), 8.1.0, GPU: Mali-G72
VLNQA00096, Samsung Galaxy S8 (SM-G950F), 8.0.0, GPU: Mali-G71
VLNQA00152, Huawei P9 (EVA-L19), 7.0, GPU: Mali-T880
VLNQA00202, Samsung (SM-N9600), 8.1.0, GPU: Adreno (TM) 630
VLNQA00163, Lge V30 (LG-H930), 8.0.0, GPU: Adreno (TM) 540
VLNQA00023, Xiaomi Mi 4i (Mi 4i), 5.0.2, Adreno (TM) 405

Fixed in version 2019.3.0a1