Steps to reproduce:

1) Download attached project 'TestPortraitBug.zip' and open in Unity
2) Make sure Default Orientation is set to 'Landscape Left' in Player Settings
3) Make sure Development Build is disabled in Build Settings
4) Make sure Lock Screen on a device is set to Swipe
5) Build and Run project on a device
6) After TestScene' is finished to load, lock device, wait ~2s and unlock it
Note that half of the screen will be black for a second or two

Expected result: Transition from lock screen to application should not make half of the screen black
Actual result: Half of the screen is black after unlocking device(check attached video)

Reproduced with:
5.3.7p4, 5.4.5p4, 5.5.4p2, 5.6.2p4, 2017.1.0f3, 2017.2.0b3

Devices under test:
Reproduced with:
Lge LG D855 (G3)*, OS:5.0, CPU:armeabi-v7a, GPU:Adreno (TM) 330, Build:lge/g3_global_com/g3:5.0/LRX21R.A1445306351/1445306351:user/release-keys

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

Lge LG H850*, OS:7.0, CPU:arm64-v8a, GPU:Adreno (TM) 530, Build:lge/h1_global_com/h1:7.0/NRD90U/170931540650d:user/release-keys

Not reproduced with:
Google Pixel XL*, OS:O, CPU:arm64-v8a, GPU:Adreno (TM) 530, Build:google/marlin/marlin:O/OPP2.170420.019/4021594:user/release-keys

Google Pixel*, OS:7.1.2, CPU:arm64-v8a, GPU:Adreno (TM) 530, Build:google/sailfish/sailfish:7.1.2/NJH47D/4045516:user/release-keys

Note: Mostly occurs LG devices because of theirs swipe-lock design