To reproduce:

1. Download and open attached "Puzzle City.zip" project.
2. Build and run for android.
3. When application starts, minimize it before splash screen starts appearing.
4. Maximize the application right after it was minimized.
5. Wait till the level loads.

Expected result: Application loads and UI texture is clearly visible.
Actual result: After application loads, UI texture becomes fully black.

Reproduced with: 2017.3.0b3, 2017.2.0f2, 2017.1.1p4, 5.6.3p4, 5.6.0a6
Not reproduced with: 5.6.0a5, 5.5.4p5
Regression introduced in: 5.6.0a6

Devices under test:

Reproduced with:
Lge LG H340n, OS:5.0.1, CPU:armeabi-v7a, GPU:Adreno (TM) 306,
Build:lge/c50n_global_com/c50n:5.0.1/LRX21Y/151672304cd28:user/release-keys

Samsung GT I9300 (Galaxy S3), OS:4.3, CPU:armeabi-v7a, GPU:Mali-400 MP,
Build:samsung/m0xx/m0:4.3/JSS15J/I9300XXUGNG3:user/release-keys

Samsung SM G930F, OS:7.0, CPU:arm64-v8a, GPU:Mali-T880,
Build:samsung/heroltexx/herolte:7.0/NRD90M/G930FXXU1ZPK3:user/release-keys

Not reproduced with:
HUAWEI EVA L19, OS:7.0, CPU:arm64-v8a, GPU:Mali-T880,
Build:HUAWEI/EVA-L19/HWEVA:7.0/HUAWEIEVA-L19/C432B386:user/release-keys

Htc HTC Desire 300*, OS:4.1.2, CPU:armeabi-v7a,
GPU:Adreno (TM) 203, Build:htc/htc_europe/g3u:4.1.2/JZO54K/272032.4:user/release-keys

Notes: Sometimes it takes more than once cycle of steps to reproduce the issue.

Verified with 2018.1.0a4, 2017.3.1p2