How to reproduce:
1. Open the attached project "Reproducebug_867891.zip"
2. Build and run on Android device
3. Close app
4. Open application and press lock button very fast
5. Unlock the screen
Result: App doesn't continue loading, one should see distorted image or black screen

Reproducible: 5.4.4f1, 5.5.0p4, 5.6.0b3
Not reproducible: 5.3.7p3

DUT(repro):
LG G5 [LG-H850], Qualcomm Snapdragon 820, Adreno 530, OS 6.0.1
Samsung Galaxy S 5 Neo [SM-G903F], Samsung Exynos 7 Octa, ARM Mali-T720, OS 5.1.1

Note: Using Unity 5.5.0p4 I have been able to reproduce this issue only once
Make sure that in 5.5 and 5.6 versions Splash Screen is disabled, but custom splash screen is selected
Issue is not reproducible when using default Unity splash screen